Falling out of emunah is not the worst possible aveirah
It's the first of the Aseres Hadibros, and makes one lose their chelek in Olam Haba.
I won't judge an individual because I don't know his nisayon, but the aveirah of kefirah is horrible. Let's call a spade a spade.
Perhaps you could argue that others are worse, but it's not a competition.
The fact that it's so bad is, if anything, a reason to help bring someone back to the fold, but Footsteps does precisely the opposite.