Some opinions aren't worth having a discussion about. If someone says that "all fags should be rounded up and shot" there's nothing discussion worthy there. A rape survivor is under no obligation to have a discussion with someone who says "all rape victims deserve it, or are liars, or both."

These are extreme examples to be sure, but the principle remains.

And nobody is saying "you can't say 'all fags should be shot.'" They're saying 'You can't say it _here_." Freedom of speech is not freedom to be heard.