Blasphemy requires a belief in god, because blasphemy is doing something that offends god or at least what people think would offend their personal version of god. What you need to get over is the idea that blasphemy and immorality are the same. They are not though there is considerable overlap.
If there is a god, I want to believe that there is a god. If there is not a god, I want to believe that there is no god.
