in his yard

The whole point of giving it away is that it won't just be in his yard anymore.

that’s his right

Yep, you can argue that the carpenter is within his rights. That's always a sign that the actor in question is behaving in a constructive way, isn't it, when the best defense is to run directly to the finer points of what that actor is legally permitted to do?

"That's his right" is a very narrow lens with which to view the situation. It's not a POV you'd even choose to bring to the discussion unless you had already decided on the question. It does nothing to address the real-world problems and complaints that are happening. It's pretty much changing the subject.

Would you make the same "within their rights" argument if the carpenter was Google? Microsoft?

people want him to build his bridge their way and keep using his bridge.

I don't think that's accurate. People who rely on rsync want some kind of clear path forward, the option to use something similar in quality to the older versions. If that's not the original rsync project run by the orginal rsync developer, no one will care much.

It would have been possible for the developer to turn over mainline rsync to someone else, and to go down his AI powered rabbit hole on his own. He could have done all the stuff that was "his right" without being disruptive.