You see, annalex, blasphemy is often ill-defined term. Is it a blasphemy to attack Islamic customs of terrible mistreatment of women in Islamic societies ?
Those who murdered Theo Van Gog thought so. Should we protect the murderers then because they murder in the name of Islam ? Is it a blasphemy to discuss the real life of the prophet Mohammed, including his child wife ?
When New York museum opened the anti-Catholic exhibit (featuring cross in Urine or images of Virgin Mary covered in Dung), I certainly agree it was amoral to allow this exhibit to run using public money. However, had this exhibit opened in some private gallery with private money, I would say that as much as I disapprove it, freedom means freedom (including for the views I strongly oppose).
I would let the courts decide if the alleged blasphemy was for real. The general rule should be, in my opinion, that when a speech may be offensive, the speech recipient must be warned. For example, if a book is critical of a given religion and it is clear from its cover, then one who buys the book cannot complain of being offended.
The other test is gratuitousness of offence. It is one thing to be critical of the veneration of the Blessed Virgin Mary in some theological way, another to slap dung on her image.