I'm partially in agreement with this. However, some people have beliefs which you just cannot defend. There are plenty of decent Christians, Muslims, etc. who are entitled to their beliefs and I wouldn't argue with them even if I don't think they're correct, but some people have beliefs that are just unacceptable and you can't defend these people. If your religion leads you to have derogatory beliefs about people who are disabled, gay, of a different religion to you, or whatever, then you deserve to have your opinions mocked.
Just as a random example, Mormons have stupid, offensive beliefs and I will gladly mock them. On the other hand Rowan Williams, the Archbishop of Canterbury, is a respectable man with respectable opinions. I don't agree with his opinions, but I see no reason to mock them.