In all modern democracies, one of fundamental citizen rights is that of a Religious freedom. There is no state-backed religion and there is no discrimination of people based on their religious beliefs. At least in writing, as something similar is undoubtedly written into Constitution of your own Country.
For example in my native Croatia, Article 40 of our Constitution says:
“Jamči se sloboda savjesti i vjeroispovijedi i slobodno javno očitovanje vjere ili drugog uvjerenja.”
which roughly translated means that freedom of consciousness and religion and free public display of said religion or other belief is guaranteed. Or in the US, with the First Amendment:
“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.”
This is, of course, an important right. Let’s just remind ourselves briefly why. There was no small amount of instances through history when people who had religion different than the majority was persecuted and executed. This is still practiced today in some countries, for example Burma, where intolerance, discrimination and violence against Muslims is provoked by the Buddhist community (PDF). (ah, those religions of peace …). So, I believe we can all agree that freedom of Religion is important.
The thing is, Freedom of Religion also ensures the rights of people to change their minds about their religion. This basically means, if you have another religious idea, other than the one you currently practice, you are free to act upon that idea and leave your old idea behind, you are free to change your religion.
So, this is to me evidence that as far as countries are concerned, Religion is, and should be only an idea and it should have no more privilege when it comes to criticism, than for example, politics. And we all know that a lot of politicians leave their old political parties behind, only to spew criticism on them from afar.
This is only one example. You can criticize everything, so why should only Religion be spared? Why is Religion the only thing nothing bad can be said about?