It's hard to believe there's actually a singular "who" to all this... it's a social phenomenon, and It's pretty much everywhere now. Two things are driving it, IMO:

One, people's loneliness and desire to conform leads them to parrot and pile on with whatever the group is saying, which spirals into a shit tornado of tribal behaviour that ends up defending ever-dumber ideas. You can't direct a mob once it's moving.

Two, the group's stated goal to be "nice" and "inclusive" ironically creates an in-group/out-group split: as long as you agree, the tolerance will flow. People want to stay on the good side of the equation, so any rejected voices get shunned and that clicks the ratchet ever further to one side. It becomes a witch-hunt.

I was just listening to a talk by an author (Chimamanda Ngozi Adichie) where she said "you have to be comfortable with being uncomfortable"... (You hear that sometimes when it comes to discussions about race these days—but it's often one-sided, and someone is being told to stay uncomfortably silent.) I actually think she has a nuanced interpretation to it though, and everyone needs the space to both say and more importantly to hear uncomfortable things. We need the ability to both say something honest, but potentially offensive, and also to have the grace to let it slide. It's like slack in the system, and right now we have none.