"But I think that blasphemy is a serious offense and a civilized society should offer protection against it to all religious."
Then you have to define "blasphemy" in a way that all can agree on, and which does not prevent legitimate discourse about - and criticism of - religion. I wouldn't like to be the one assigned to write the anti-blasphemy laws.
See my preceding post. I agree, it is hard. But, we managed to convict Martha Stewart on arcane stuff no one can comprehend, - why can't we have someone define blasphemy and still discuss religion? It was done for centuries, until Larry Flynt became a 1st Amendment expert.