it becomes "depraved" when it's with a man because...?
Because, as a man, I am not wired to understand what makes men attractive sexually. So, when men are sexually gratifying themselves with other men, it is 'depraved', 'wrong', 'sick', 'unhealthy', or any number of other adjectives that I can come up with to describe something out of the ordinary and taboo at the same time.