I don't think this is a lemmy.world problem as much as it's a Fediverse problem. Assuming that the only reason to block these communities is legal safety, we should figure out what is legally unsafe and see if that can be enforced on the piracy communities, or everyone in the Fediverse could also be at risk and should block these communities.
I know that the piracy communities themselves are already taking these kinds of measures to make sure they are not unsafe, so if anything is found we should solve it together. If push comes to shove, I suspect that piracy communities would rather restrict themselves than risk taking a stand and endangering others. It's not that big of a deal to skirt legal concerns while still being a useful piracy resource - /r/piracy existed in much the same state.