I know a fair number of people who are both liberals and non-Christians. They are huge into tolerance of all forms, including religious tolerance.
And yet, they think it is appropriate to refer to Easter as Zombie Jesus Day. (Because Jesus rose from the dead, for those of you who don't immediately get it.) Mock a Jew or a Muslim for his religion, and these people are likely to be all over you. It's not appropriate, it's bigoted and juvenile and no longer accepted in our pluralistic culture.
And yet "Zombie Jesus Day" somehow doesn't fall into all of those categories?
There are conservative Christians who complain how picked on Christianity is, how it's considered acceptable to "persecute" Christians but not those of other faiths, and by and large I find their claims unsubstantiated. But this is one example which proves the conservatives right: it seems to be acceptable among some to mock the holiest day in Christianity, even though similar behavior toward other faiths would be immediately condemned.
It's name-calling, pure and simple.