Well sure they can convince themselves of it, just like they convince themselves of reasons to not have players who are overly vocal about politics or many other things. They have 60+ players to bring into harmony under difficult, pressure filled conditions, within relatively confined areas. Unless a player is uniquely talented, why take the player with a lot of extra baggage?
They need a player who is a solid player and says; "By the way, I'm gay." and then goes about his business as a football player. It will be next to impossible to break the ice with a guy who says, "I'M GAY!! and , oh, by the way, I play football."