You wrote: "How so? If we have freedom of religion, and freedom of speech, then we also have freedom to criticize other people's, or even our own, religions."
Category mistake. The point was about moral responsibility. Your answer was addressed legal freedom or liberty.
I would argue against almost any legal restraint of speech except for felonious or terroristic threats, libel, fraud, and treason.
I would also argue against any restraints on such speech-related activities as boycotts and protests directed at offensive broadcasters. Here again, it's not a matter of legal censorship, but of public free-speech response. If you don't like a broadcast you can turn it off---- OR you can boycott their sponsors and shut 'em down, and more power to you.
But I heartily agree that it can be immoral (I didn't say illegal) to ridicule and defame other persons, religious or not. Not immoral across the board, but immoral when it involves an element of humiliation, degradation, or falsehood.
There is a sin called "detraction," which means revealing something which is damages or destroys another person's reputation, UNLESS there is a sufficiently grave reason to do so.
Examples: it is NOT the sin of detraction to reveal that a pastor lost his last two appointments because he embezzled money from his congregation (because there's sufficiently grave reason for his present congregation --- or at least their parish council --- to be informed of that.) But it IS detraction to reveal this this pastor committed adultery 15 years ago. That's none of the congregation's business. Nor of the general public.
And to reveal such a thing in a humiliating, mocking, and totally public way would do immense harm to the pastor, his wife and family, and his congregation. It could also trarnish their whole denomination, and expose innocent persons to suspicion or mockery.
To hold the offending pastor up to public contempt and ridicule in order to destroy his reputation would be --- even if not legally actionable --- a gravely immoral thing.
Sliming and degrading the Virgin Mary and the Pope in the way the South Park did is clearly morally offensive. If protests and boycotts cause them to deep-six this segment permanently, then hooray! Another victory for free speech.