I think for a non-believer to say "God Bless" reveals in stark detail the profoundly deep, entrenched hypocrisy of all atheism and why it threatens to bring about the collapse worldwide of civilization.
But I could be wrong about that.
You're close, but it's not when they say "God Bless." It's when they say "Jesus H. Christ."
But what about when Christians say things like "gosh darn it" or "gee whiz"? They're using phrases which are close to phrases which might be interpreted as using the Lord's name in vain, but just enough different that they can get by on a technicality. That's a bit sneaky.
To use the word "damn" after the word "God" is especially bad in some people's eyes. So, if someone gets angry about something, they might say "God bless it!" when they really mean the opposite.
I have a feeling it must lead to some kind of paralytic confusion up in Heaven, as all those administrative personnel are working overtime processing these endless requests for God to either "bless" or "damn" something or someone.