Yes, but that decomposes into blasphemy (against a deity) and defamation (against a person). For example, Jehovah probably doesn't exist. That's blasphemy, but it says nothing about those who believe in Jehovah. It's optional to include defamatory swipes at believers.

For comparison, recall that Santa Claus also probably doesn't exist, and examine your emotions to see how you feel about the contrast between Santa Claus and Jehovah.