The whole point of IT isn't to argue against the blackpill, the subreddit exists solely so there's a subreddit for people to bully ugly, lonely and mentally ill men who haven't experienced intimacy. Since virgin shaming is now seen as non-PC, they resort to the next best thing which is socially accepted. Incels aren't a protected group.
There's also a certain mindset among these people, which is the old traditional notion (even though these people are liberals) that men are supposed to 'woo' women and not the other way around, and incels are just failed men and that its okay to bully them. Essentially its a form of telling social rejects that they should know their place, they shouldn't rock the boat by talking about the blackpill, and they should just ideally kill themselves.
Since none of that is socially accepted they just veil the actual purpose of the subreddit.