Opt-in denylists with pre-populated categories would be a reasonable feature. A frontend author trying to trick users into thinking there’s a technical issue with servers the author doesn’t like is presumptuous and disrespectful of the user.

People did similar stuff with Mastodon clients when the far-right microblog service Gab migrated its backend to a Mastodon fork and I didn’t like that either.

I think it’s best we just maintain some recency bias when it comes to how harshly we judge people for their past internet behavior. If you were an asshole ten years ago and haven’t acted that way recently, I’ll just assume you were 12. We were all 12 once.