I disagree just due to the aforementioned network effect. Numbers with social media have a snowball effect, where people make their decision on whether or not to participate based on existing levels of activity. What sets Lemmy apart from stuff like Lobste.rs and HackerNews IMO is that it’s integration of federation gives it potential to break out as a serious alternative to the platforms rather than catering a specific niche, so I’d say the snowballing is important also since it has the potential to help bring up the rest of the Fediverse.
Given Lemmy’s reputation as being a platform run by communists, the fact that such a hardcoded filter even existed to begin with, and also per-instance blocking/slur filtering, I’d think that should be enough to keep them away and stop them from polluting the communities associated with the flagship instances, then again I’m not an admin so I can’t say for sure. It’d also help the issue you mentioned regarding ambiguity of what slurs to include, since each community can decide that for themselves.
Isn’t instance-blocking alone sufficient for being able to prevent the environment from being overrun? I understand the hesitancy to platform reactionaries, but as it stands the network effect is easily the biggest hurdle the Fediverse is going to face. Right-libertarians and actual reactionaries might be a net negative on the main instance, but as far as the software itself goes, numbers are numbers, and could end up making a world of difference.
Let them form their own circlejerks away from everyone else and have slur-blocking be on a per-instance basis, after all that’s why the federated design works so well.