That's true. But people engaging in "casual" conversation over beer aren't inciting each other to commit violent acts of hate.

But in those rare instances where a bar crosses over into openly supporting that type of speech, the police start taking an interest and monitoring that bar and its customers. And if a line gets crossed with respect to incitement, conspiracy, etc., the local municipality will usually pull the bar's liquor license and get it shut down to prevent future such crimes from being organized or incited at that bar.

So, really, you're actually quite spot on with the bar analogy. 4chan/8chan are exactly like a skinhead bar that's getting shutdown because the customers kept inciting each other to kill people and actually followed through.