Also point out there is a line where 'free speech' drifts into criminal conspiracy. If a group is using your platform for criminal conspiracy you have an absolute right to kick them off.
For those interested, the relevant search term for United States law is "compelled speech".
I am an old school hacker/programmer and for some reason I can't rise above 300 karma on HN because of how much people hate discussing free speech. In another thread someone called me 'Joseph Stalin' for advocating for free expression.
I ran a Greasemonkey script for several years that removed all karma figures from HN. I don't anymore, but it helped me develop the right mentality early on.