They should be pretty on it for security updates. Librewolf is also hardened compared to upstream Firefox so if security is a concern, you’re probably better off using the fork anyway.

If it’s so easy to “use wrong” then it’s badly designed software.

Nobody’s saying it’s mandatory. People don’t want their web browsers to be full of bloated AI slop. Why should there be the AI components of Firefox on my hard drive if I’m never going to use them? Why should my web browser be full of low quality features I’ll never use? It’s enshittification. Not to mention the very quote you’re pasting specifies that it’s opt-out, not opt-in.

It increases the workload for fork devs the more crap they have to remove from upstream and the more the fork deviates from upstream.

I don’t know what websites you’re using, but default uBlock Origin works completely fine with all the websites I visit, and it doesn’t use AI. It just uses blocking rules.