It's not protecting God, really. There is a special level in hell reserved for those that willingly mislead others spiritually. Unfortunately, those that are misled also suffer for eternity, as ascribed by the Bible.
While the perpetrator of blasphemy deserves their fate, many of those who would be misled may be saved by the identification of the falacious teachings.
Please note - I am only discussing the basis for determining something to be blasphemous, but only identifying a rational basis for the religious crime of blasphemy. What one church or another decides is egregiously misleading from the "truth" has often been beyond me.