Well, if the rules are the same as an actual public square, then outgroups can participate in exactly the same way as they do in actual public spaces, governed by laws enshrining freedom of expression. That is to say they may be insulted and ridiculed by members of the public because we as a society have decided that we don't trust any authority to moderate public discourse.

These conditions do in fact represent "actual" freedom. Basically if you support people insulting and ridiculing Nazis (which I do), you should support them insulting and ridiculing anyone else on the same principle.

Sorry, I'm confused now, are we talking about a place where people exchange

> civilly-expressed criticism of themselves and their worldview [0]

or where they should expect to be ridiculed and insulted? And why would anyone sane want to regularly participate in the latter?

[0]:https://news.ycombinator.com/item?id=31167326

Yes? If you're going to a place where freedom of expression is a primary value, then you should not be surprised by any kind of expression, from cheerful agreement to hateful bile. I agree being rude is well... rude, but people should be free to choose for themselves what rudeness (and directed at whom) they approve of, don't you think?

As to why people would want to participate, I suspect it's for the usual reasons: to accomplish a goal, or to gain influence and social status.

Edit: Surely you agree that sometimes rudeness is warranted, and that people in fact are rude on Twitter?