If they're not outright illegal, they'll be outcompeted by sites that don't require you to install special software to visit them. Those sites will have a marginally higher chance of being subpoenaed than before. They'll have to tell their host who they are (which is already the case for non-onion sites) and if they publish Nazi propaganda the police may knock on their door.

You know, exactly how it was 25ish years ago before the regulated Internet era. We had an internet back then, and people were slightly more constrained with what they do on it.

Over time, people tested the boundaries of what they could get away with, found they could get away with a lot, and then got away with a lot. Now we generally agree it's gone too far and the boundaries need to be set tighter. This is the cost of that.