Seems mostly casual players, although there is at least one GM (Ben Finegold) who was very vocal with this stance, until recently.

I suspect the people most troubled by this new wave are those who use chess as a crutch for their own identity. If chess is viewed as a game for sophisticated, intelligent, cultured, etc, people, then they as chess players are also sophisticated, intelligent, cultured, etc. When that image of chess is threatened then they personally feel threatened.

Personally I'm glad to see the sudden rise in popularity, and don't care who's playing as long as they're having fun and not ruining it for others. (I'm at a master level.)

Probably the best way to understand it is similar to the complaints that Stack Overflow is filled with basic beginner questions on the front page to the extent they drown out any questions with real technical meat.

Hikaru teaches the controversy:

https://www.youtube.com/watch?v=jaavgNN9b4Y

One grandmaster described the streamers as having "negative talent in life".

You mean the barely GM, 50-sub Andy?

It was Ben Finegold. I'm sure a lot of people think this but don't want to say anything to dissuade people from learning chess. Games by 700 rated low skilled players are really really boring to me but good for twitch viewers for enjoying them. Don't really care.

He definitely fits my description :)