I take your point, but it's part of Christianity being the dominant religion in most of the countries that people here live in; it's part of most of our heritage, like it or not, so people feel that they can mock and deride it. The fact that Christians can, by and large, tolerate this abuse, without burning effigies or worse is a credit to them.
The reason why if you were to mock and deride Jews in the same way, you might be condemned as a Nazi, is that the recent history of the Jews is pretty harrowing; most people are concerned not to appear as if they condone what happened in the holocaust. Making a joke about black people isn't even the same thing: it's a matter of race, not religion. I think most Buddists can probably take a joke at their expense.
I do, however, agree that a lot of the mockery of Christians is pretty cheap. For instance, every time there's a thread on here about favourite works of fiction, some joker has to come along and say 'the Bible', and probably thinks they're being really edgy and clever by doing it. Of course, if they believe it is a work of fiction, and superior to all other works of fiction, that's fine; but I'd imagine nearly every time it's a cheap swipe.
But as I said, it's because of Christianity's dominant position that people knock it. People always go for the number one. Coca-Cola gets its business practices ripped to shreds, and rightly too, but no-one ever bothers looking in to Pepsi. McDonald's gets picketed, and leaflets distributed about it's activities, but I expect that if anyone looked in to Burger King, they'd find very similar things. Of course, I'm only guessing, but the point is that being the most popular in a particular field will always make people want to find negative aspects of what you do.
I can't imagine there ever being a Christian holocaust, because I don't see any true hatred in nearly all of the mocking and derision, just annoyance and a bit of fun. I'm not a Christian: although I do think that a lot of the negative comments made against them are petty. But you know, they can take it: and as I said, that's to their credit.