LR I don't know about the organisation you mention but you say it was a long time ago. I would have thought they'd have had to find some sort of independent radio station to broadcast their stuff and even that would have been short lived because of public outcry. People like that generally keep their views and activities strictly secret. One argument in favour is that if they go public, at least they're known, and they have the right to say it if not to act, but most people don't want to turn their radio on and hear it. These are extreme minorities though.
(I'll just mention it has been said to me that because I (& presumably some others), find a concept disgusting is not a reason to ban it; in other words, reasonable, logical arguments must be produced. That seems fair enough on a debating forum.)
Most free speech issues would be political, right or left, social & justice issues, maybe some religious. In the distant & not so distant past, the abolition of slavery, emancipation of women, cessation of capital punishment and decriminalisation of homosexuality were controversial issues which not everyone wanted aired but, thankfully, were allowed.