The question is valid. A sane person should never divorce his wife for just being mangalik. But....
Before you start bashing the guy.. maybe he had his reasons and was emotionally unstable when he said all that. Of course it was stupid to put it on FB, but people do stupid things in life when they are emotionally unstable.
From little knowledge I have, I think Mangalik people are belligerent by nature. They argue and confront on almost everything. So maybe the guy was tired of his wife arguing and fighting with him everyday. My "speculation" is as good the rest of you.
You should have brought this discussion without giving out the identity of the guy in question. That would have constrained the argument to the superstition part and not the guy himself.