Yes you can. And you should criticize, make fun of religions. Does not matter if it offends everybody else's sentiments. Until and unless there is no physical harm done, no targeted mental torture of a particular group of people, no hateful actions undertaken, till then, everything is acceptable. On the other hand, desecrating a grave, harming people or cannibalism, as you mention, are inhumane acts which actually cause harm to others.
Now, can you see the difference here?
Religion is an idea. The whole concept of trying to understand and justify our existence through a make believe system of religious traditions is simply the creation of a scared, confused, belligerent human mind unable to fathom the vast emptiness and mind boggling scale of the Universe. Its all a fantasy. The day God or Gods, if they really exist, actually appear and say that one particular way is the true path, then religion will become a reality. Till then it is just a concept, an idea.
And like all ideas, created by the human mind, this concept too is open for criticism. If it weren't for our ability to make fun and criticize, we would all still be hearing about boats falling off the edge of the earth, riding dinosaurs and hunting mammoths on the great plains of a land supported on infinite number of turtles stacked upon themselves.