TL;DR Discord loves to present itself as a company run by a few gamers just like you. The service aggressively advertises itself as "for gamers" with the hope that this "reputation" alone will propel Discord to the top. This has worked really well. The Discord team has refused, however, on multiple occasions to take certain steps to protect their userbase, described in more detail above such as adoption of E2E encryption or going open source. Instead, the Discord team states clearly in their privacy policy that they will gladly hoard a plethora of data about their users indefinitely, loosely claiming to only delete it when its no longer needed. The data they collect and store includes (but is not limited to) full chat logs, all chat media, a list of who you chat with, email address, IP address, device ID, behavioral analysis, activity tracking on the service, pulling info from social media accounts you link, and much more as stated above and in their Privacy Policy. Discord shares this same data with all of its partners, affiliates, agents, and "Related Companies" while lazily instructing you to check their privacy policy to find out what happened to your information, as its no longer any concern to Discord. In addition, Discord goes further to say "Developers using our SDK or API will have access to their end users’ information, including message content, message metadata, and voice metadata". Their very vague "information" wording allows Discord to send whatever they please while, of course, leaving it up to you to go check their privacy policy and figure out just where and to who Discord sloppily throws your data around. Discord continues to show little to no progress or effort in considering open source code, strong end-to-end encryption adoption, or even something as simple as allowing the deletion of an old account. It is important to note that while Discord allows the "deactivation" of an account, their support team will happily inform you that they do not delete your data and your account cannot be deleted. This data is again stored for an indefinite period of time.
Discord is proprietary spyware. Using it means endorsing and legitimizing it.
Discord relies on its reputation to lure its victims. Despite just starting out as a way for 
to mingle in chatrooms and VoIP rooms, Discord has now expanded to any sort of purpose, even extending to schools where students will use Discord for clubs as well as online projects where communication is done over the platform.
The reliance on Discord is dangerous. Any thing you type or do in this program is recorded for the highest bidder (that be your government or private data brokers). The interface and UX is designed to keep you in the app for as long as possible.
There's no way to "smartly" or "responsibly" use Discord. One way or another, Discord will extract value from you. It's not just about you, but about everyone who uses the platform.
Solutions
There are no "alternatives" to Discord. I'm not going to try to fool you by saying there's a magic bullet to defeat Discord's presence in western society (other than socialism and 
). But that doesn't mean there aren't ways to help.
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Matrix: A decentralized messaging protocol. It supports video conferencing on its main instance as well as support for the Discord "Server" functionality. Easiest solution for a drop-in replacement.
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IRC: The one that came before Discord, community networks can be used if you need to communicate and is just as secure as Discord (public chat rooms with zero end-to-end encryption besides TLS)
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GNU Jami: If there was a magic bullet, this would be it. Completely decentralized, peer-to-peer messaging network that is device based. It is a GNU package, possibly the most guarantee for freedom you can get in this world. The team is small, but if you need somewhere to host your leftist activities that will require more than a court order (or a simple bribe) to de-anonymize by state and non-state (those funded by other states) actors then this is it.
Conclusion
This is a post for self crit. If the service is free of charge, then you're the product. Any leftist should take steps to eliminate their dependency on Discord and proprietary messaging programs. Also any leftist should spread this message and inform others about the risks of using proprietary software.
We should also take Discord as a lesson in how to identify the dangers of proprietary programs and why it could make us vulnerable to abuse (which as we know in a capitalist society, is coming one way or the other). Discord isn't the lone offender, but an example of how nonfree software will always pose a threat to a free and democratic society and only benefits the bourgeoisie.
Let this be the last thing I have to say about this accursed program
The complete absence of any understanding of free-as-in-freedom software within the broader left has been an absolute disaster. At best, you have various technolibertarians who at least understand that FOSS is one way of combating corporate control over social life even if they overly emphasize the "OS" part and believe that FOSS is sufficient. Meanwhile, you have organizers using Google Docs and leftists getting very defensive about ditching Windows for Linux. Boo hoo, I can't play my AAA slop or MOBA with kernel-level anti-cheat detection.
Having said that, I do think leftists who actually understand what libre software, gratis software, and proprietary software are have a responsibility to guide the technologically illiterate and semi-illiterate among us. Just telling people to install Linux Mint is fine, but there should be more effort towards actually guiding people (ie compiling and creating guides). And it has to be actual guides, not "you need to learn how to think methodically stupid" STEMlords like to trot out. I feel like /c/libre ought to be geared towards creating guides of FOSS alternatives towards popular proprietary software such as what you're doing now with Discord. The main barrier is that we don't have a critical mass of users on Hexbear who give enough of a shit about FOSS to pump out guides, meaning the responsibility of creating guides will fall on the shoulders of a few people, who obviously have to juggle their free time with school and job responsibilities.
Linux Mint has a guide on how to install Linux Mint. There's some things that could be improved (Ventoy/Rufus is better than Etcher for Windows users. They mostly picked Etcher because Etcher is available on MacOS as well and they don't want to bog down their section of the guide with the many ways of creating a boot flash drive.), but it's a good template. Ideally, it should be a group effort so it isn't just one person who has to shoulder the responsibility. I'm not sure how this would be implemented in Lemmy.
Oh god tell me about it. If you ever bring it up you become a "evangelist" that likes to annoy everyone or just ignored outright.
"You will allow me to install an always-on rootkit on my computer, to let me not do so will be infringing on my rights!!!"
I agree, it only takes one person who's knowledgeable about free software to educate the entire group. There should definitely be more guides but there's simply not enough people right now to write them. I've personally always wanted to write a Linux Mint Deprogramming-style guide for a while now but I've been waiting patiently for their next major version to release before I do so (and also for various things to be resolved like Nvidia graphics support and such with NVK).
There's still a lot that needs to be done at least.
I agree with you. The one feature that Lemmy is missing from Reddit is the Wiki. Often, on Reddit, the wiki would grow stale over time, sure. However, I think spaces like Hexbear and Lemmygrad are entirely geared towards maintaining a large repository of structured content. In this context, it would be centered on succeeding from the tech-feudalist infrastructure, but it could also be content on combating liberalism. Things like Ibis could be that repository, but development on that end is slow currently. When my parents needed a new computer, I went to a local surplus shop, bought a really dope used computer for almost nothing, and put Linux Mint on it. They've been using it for years at this point, and I've only ever needed to provide support a couple of times. So the usability, in my personal experience, is very high.
I think part of the issue, however, is hosting, support, and maintenance. There are plenty of awesome self-hosted solutions out there, but the issue is the "hosted" part. For the average person, and of no fault of their own, that is a huge hurdle for them. Suggesting something like Nextcloud as a replacement for Google Docs is the easy part. Getting them through the installing/hosting aspects of that is the hard part. I think there is a "trust" issue to tackle too. While it's easy to point out the trust issues with things like Google, Twitter and Facebook, most people I feel view themselves as small fish in a vast ocean of users. It leads people to think, "Why would Google personally target ME?" It's impersonal to them, and there are so many people who work at Google, so they believe there must be some kind of compartmentalization that protects them from having their personal information viewed and acted on. On the other side of that coin is convincing people that "some random group of people" can be "trusted" with your chats/docs/posts/dms etc. The DMs on Lemmy are not encrypted, and with a simple SQL command, anyone with system access can query your DMs. Lemmy makes no illusions of security within DMs though, so it's not a huge issue. Someone who has access to the system hosting Nextcloud can access the files created by the users (to my understanding). The question of "Do I trust Google with my personal documents" vs "Do I trust Timmy with my personal documents" is obviously a very different set of questions. Naturally, this leads to having to do the compartmentalizing yourself, and having a space you control for your personal stuff and a collective space for your activism/organizing stuff. Which takes us right back to the "hosting, support, and maintenance" question.
So the guides are not simply about setting these services and softwares up and using them. It's also about changing how you think about services generally. We would need to establish a kind of, wading into the pool, guide and on ramp. Guides that get you started with things like switching apps to FOSS alternatives (like switching to Fire Fox derivative browsers), to switching to FOSS Operating Systems, to fully "De-Googling" your Chat/Docs/Calendar/Email usage, all the way down to setting up hosted services for you, your activist groups, your family, your friends, whoever.
This is something I'd help with in whatever capacity I could. I already self-host a number of services for myself.