Ridicule is a tool. So it can be used for good or bad.
I think that we have to accept that all ideas can and sometimes should be subjected to ridicule as soon as they enter the public space. Religion is just a well organized collection of interconnected ideas and I see a far greater danger in providing it with special privileges, then any potential harm inflicted through its ridicule.
That said, I think the reason why there is objection by some to the ridicule of religion is perhaps because faith in a prophet or deity (I would imagine) is probably a pretty hard thing to maintain at the best of times. And it is obvious that for many people their faith is a deeply essential part of their lives. It also seems pretty clear that for some people they really need to believe that whoever it is they decide to hand over their own moral compass to is pretty much infallible. The devout deeply want to be close to god, they deeply want to please god, they deeply want to do the right thing. To do so they believe that they have to follow the rules and regulations of prophet X.
So along comes the non-believer ridiculing prophet X or some aspect of the faith, and if they can’t defend their faith in any way that is going to hold water with the non-believer, they sometimes resort to either attacking the non-believer, or their motives, and usually they also challenge the very notion that “ridicule” is an acceptable form of discourse.
I think this has something to do with how the person ranks the defence of their faith relative to what is being ridiculed. For instance, if what is being ridiculed is some aspect of their religion that is pretty difficult to defend (the Catholic church’s handling of the condom and aids issue, or for instance the atrocious handling by several religion’s of paedophilia scandals), then they might just let the issue of ridicule go. But if it is some aspect of the prophet’s life or the prophet’s teachings, then suddenly ridicule can become “unacceptable” very quickly.
So my view about ridiculing religions is mixed. I think it all comes down to what exactly is being ridiculed and why.
So in short, when religions perpetuate ignorance, bigotry, or suffering. Open season.
When religion’s followers are subjected to bigotry, coercion, or suffering, then open season on their attackers.
It’s all about protecting people above and beyond protecting ideas, dead prophets or gods. Unfortunately, sometimes that can mean ridiculing ideas that people care about.
whether or not ridicule is the best way to bring about a desired change is another question, but probably once again comes down to the context of the situation