Further, reddit is built from the ground up to force consensus. Counterculture cannot exist on the site by definition, as anything prevalent on the site is there by consensus.
That makes no sense - consensus must exist within a counterculture for it to be definable, therefore counterculture and consensus can coexist.
Being "prevalent" has no bearing whatsoever on being a counterculture. It's entirely possible for a counterculture to have a subreddit and not be prevalent. The vast majority of content on Reddit never even touches the frontpage.
You could say that a counterculture can't exist on Reddit that runs counter to the platform's terms of service, and that might be true, but it's also conditional.