It comes down to “they do not think like I want them to or they won’t agree with me, so I will downvote posts.”
Controversial topics are even more downvoting just to downvote.
The self-built echo chambers are already constructed; self-censorship and anything outside of their views and sources are dismissed, labeled, and smeared so as to not think about the information being shared.
It happens everywhere; the status quo is welcomed, while anything outside of it will seem controversial or extreme.