I often use a commercial VPN service, which I suspect is not rare among Lemmy users. Most of the time, I'm able to post to lemmy.world, but on occasion I am not. The default web UI provides zero feedback, just a spinning submit button forever, but if I look in the browser dev tools, I can see it's being blocked.
I understand that some limitations are necessary to prevent spam and other abuse, however this is a very blunt instrument. The fact that I have a 10 month old account with consistent activity should outweigh any IP address reputation issues.
Perhaps the VPN limitations could be narrowed in scope to cover only account creation and posts from young accounts.
It is radically public. It's designed to broadcast your content to hundreds of other peoples' computers running all manner of different software which might then rebroadcast it to yet more. The whole architecture is oriented toward spreading things far and wide, and what tools exist to restrict the audience or retract content already shared are little more than polite suggestions.
That's not a flaw, but people using it should understand how it works so they don't run into surprises.