If a group of pedophiles wants to say they want to have sex - then YES - ABSOLUTELY they should be able to. Allowing people to say stupid shit isn't agreeing with them, it is the courtesy afforded to them to listen if their ideas have merit or not.
As soon as you put controls on it, you make exceptions, and the weasels will always find a way so that they can have their free speech but you can't. Much like how Islam is using hate speech to control criticism of their ideas whilst allowing free range on their criticism of everyone else.
Free speech is BINARY. it is either on or off. There is no middle ground.