"All those, even supposedly intelligent people, who believe in "god" have the mentality of children. Grow up!!!"
That's a bit too obnoxious for my taste, but the initona words, "Why would an unbeliever be concerned with the question?" are valid.
Your question suggests that god/God exists and heaven is a real destination. If you're right, then Biblically, it's easier for an unbeliever to get into heaven than someone who believes but doesn't behave propperly. That sounds to me like it's possible, if unlikely.