4chan has a pretty hard and fast rule of contrarianism, in large part because thats what keeps posts from falling off the front page.

They don’t use votes there, posts that get replies move to the front page and fall down until they hit 10th page and disappear if they don’t get any.

As a result, 4chan will go against whatever the largest voices in modern culture are saying, which for over a decade have been the left wing/liberal ideology. Before that, they were very left-leaning because we were in the Bush era where culture was very traditional/right leaning.