I mean, it depends what the reason is for them to do that. If it's just because they are cheaters and they are mad they can't cheat anymore, like many people in this thread seem to think, then yes that's stupid.
However, from what I heard, there were still plenty of cheaters and it didn't do much about that.
The biggest thing this anti cheat did (again from what I heard) is making the game unplayable on Linux / Steam Deck. If people are protesting because of this, I think they're right.
It really depends on the reasons and the context.
I agree that cheating is horrible on GTA V, but it's actually even worse on RDR2, I gave up because of that, I kept getting killed by cheaters.
At some point there was even a player who made me unable to move, and started f*cking my character (female character), and then he gave me flowers...
Sometimes people put you in a cage, make you explode etc... It can be funny once, but when it's all the time and you can't play normally anymore, it's awful.