When did this happen?
If you mean the people who dislike him; a lot of people were slightly above his age demo when everyone hated him for becoming popular screaming at horror games. They didn't grow up with him and so they have no sense of loyalty to him.
I assume the reason he's a massive pillar of internet culture for people under a certain age these days is because the little kids who watched him when they were in his demo are in their late teens/mayyybe early 20s now. You have to remember though that Terraria came out around that same time and not everyone who got into it was a kid in pewdiepie's age demo.
If you mean the people coming to defend him; I think it would be an unfair accusation to make of them too. Both groups should be more than old enough to have accounts at this point.
If this actually happened that's a different story, but from what I've seen it's just an assumption.