Are there any legitimate reasons why homosexuality is seen as bad behavior?

By legitimate I mean practical, non-religious reasons. The only possible faults I can see is that it can be exploited as a tax loophole and that it takes two individuals out of the reproductive cycle, but I think that those reasons alone are not enough to ban LBGT marriage considering there are millions of homosexual people it could benefit and that we are now facing an overpopulation crisis.