not everyone's logic works the same way. Strict self-interest doesn't provide for the improvement of society, it's what compels people to seek wealth, usually at the expense of others.
without emotions, how will humanity continue to procreate? What kind of parent doesn't love their children? And if there's no love, there's no marriage. what kind generation is going to arise from these loveless single parent upbringings?
that said, you should check out
Nietzsche I know you probably didn't mean parents shouldn't care about their kids, it seems like you'd agree with his brand of philosophy.