Homosexuality has been around forever. I'd think that even during prehistoric times when a woman wasn't around, men would engage in sex. Greeks and Romans did this when on military campaigns. And we all know about Sodomy and Gonorrhea from the Old Testament.
I never had a problem working with gay men as they were comfortable in the working environment knowing straight men knew they were gay. I have almost always had a problem with lesbians however. They actually dislike men. They actually dislike straight women (regard them as slaves).
Most straight women I know are uncomfortable around lesbians as well. Lesbians often demean straight women and act "butch" around them trying to assume a male role expecting the straight woman to comply by submitting or leaving.
Mental disorder? Let me see. Gay men use their mouths and anuses as substitute vaginas. If you want sex then why settle for a filthy ass hole. Go get the real thing. There is plenty out there and in our loose culture, more than willing to participate. Lesbians are more often driven to hate men so they go after women with a like past. You'll quite often see two divorcees with kids who are living in a lesbian relationship.
I do not like companies that suggest, "we love gays and lesbians" as part of their hiring practices. What you do in your own bedroom shouldn't be a consideration for employment.