Wow, that sounds like a really challenging situation. It's unfortunate when members take discussions to such extreme and offensive levels. Moderating such topics must be quite a task. You should do what you have to do... "moderation"!
I'm too lazy to find the exact quote, but Theymos said "the aim of this forum is to be as free as possible".
Yes you are right theymos always talks about free speech and the quote you are referring to, I guess is the below one.
The things on the forum which encourage spam are allowed mainly because it's part of the forum's mission to be as free as possible.
But at the same time theymos advocates about much needed moderation too, he said it many times that
"free discussion" is not "unmoderated discussion".This forum exists to provide a platform for the free (but ordered) exchange of ideas. If you have an idea to express, then it is probably possible to do it here as long as you follow the rules.
the forum's mission of hosting free discussion of Bitcoin and related topics. (As explained above, "free discussion" is not "unmoderated discussion".)
everyone should be free to express any idea unless doing so infringes on the equal right of others.