Most of 4chan boards aren't really that bad though.
But it seems you're "implying" that if we weren't there we'd be somewhere else the same or worse. I suggest there are many better places we could be. What we do there isn't a function of ourselves alone. We are a midpoint between ourselves and our environment. I would much rather go the playground and kick a soccer ball around or play basketball, but there isn't one around open after dark :(
And I can't stand the egoic virtue-signaling/posturing on fb so I go to 4chan to get a more down-to-earth conversation experience. If i melt down on there, no one cares. My FB world is completely uptight and ready to ostracize on a hair trigger. Of course 4chan is also full of people faking badassery, but it's not attached to individual egos. That's what's amazing about anonymity that moot could never articulate: it doesn't make much sense to lie, because it doesn't really increase your standing because no one knows who you are! So people are much more honest and forthright. yes, that's often ugly, but it's better to know about than to fear it.
Now the part that anonymity doesn't solve is that although the individual ego is dissolved, the way is paved for group egos to form. And as we've seen, especially on /pol/, these collective identities have flourished.
There needs to be other sites that don't have usernames in any way. Even if you attempt to ignore it, it somehow is always relevant. Somewhere such as Reddit in particular always comes down to being a popularity contest and it will skew what people are willing to say in order to get the most likes.
This is an important note that I feel like not enough people understand. Too many people just think 4chan, and then think of all the messed up stuff on something like /b. There is lots of stuff on 4chan that is completely normal and not toxic/illegal. Although, I will admit that I usually just browse reddit, personally.