>I would still hesitate to say that we should lay the blame on these forums though, or undeniably conclude that that's where we should be making changes to prevent such problems.
I wouldn't say lay the blame on the forums for the actions for their members, however I do think it would be somewhat justified to lay the blame on forums for knowingly allowing these hateful ideologies to spread to more and more people due to their lack of action/moderation.
It's been shown that banning hateful subreddits reduces the amount of hate speech on the site by users who used to post on those banned subreddits.[1] It's hard to say if those users simply took their hate speech to some other website, but even if they did their sphere of influence would then most likely be much smaller than it was on reddit.
>If we hold free speech as a principle in high regard, we shouldn't so easily sacrifice it.
This is a difficult topic but I think that there definitely should be some limits. After all we're talking about what rules private companies should have for what kind of content is allowed on their websites (i.e. what content they are okay with hosting on their servers) and not what kind of content the government should allow/disallow.
A viewpoint I found interesting (and reasonable) in regards to limiting speech is Karl Popper's paradox of tolerance.
"Less well known is the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them. — In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant."
[1] http://comp.social.gatech.edu/papers/cscw18-chand-hate.pdf