Its obvious what is good and bad here. But do some roleplay; Its 15th century CE, and you (and all the people) have been conditioned since your childhood that the christian god is one true god and that the christian god is good.

Now if a person declares something "blasphemous", everyone will think that the person is on the "bad" side.

Setting a precedence lead to ugly slippery slopes and keeping to the absolutes in the guidelines is generally more inclusive.