Well, sin or disordered temptation.
Look, if there were a “gay” mass held for, say, a weekend retreat or at a “homosexual chastity conference” or whatever, I doubt many people would have a problem with that.
** After reading some responses here, I doubt that. Just my opinion though. **
However, having regular masses for any group of people who have their own particular temptation or disorder defeats the purpose of the mass. The liturgy is the work of the people, not just the homosexual people or the alcoholic people or the fornicating people or whatever people.
** Why does it? One of the purposes of the Mass is to strengthen your faith. Help you get closer to God. Wouldn’t someone who according to the Catholic Church can never even go on a date or kiss need all the help they can get and maybe need an extra Mass a week? Why not have one that is “dedicated” to them? Let them feel like the Church, that is so hard on what they can and can’t do, is trying to help them? Let them feel the love of the Catholic Church saying “Hey, we’re here for you. We’re here to help you abstain. You’re not alone. You don’t need to go and have sex to feel love. You have the love here.” **
So when someone says, well, other people can come to a “homosexual mass”, that is being intellectually dishonest. Of course anyone could attend, but the purpose of such a mass is to be selective in who attends, namely homosexual persons i.e. those with a sinful disorder or who are tempted toward a sinful disorder.
** Not really, have you ever been to a children’s or teen Mass? I know of people who attend those Masses because that’s the best time for them and they are adults. No one cares. **
Why is this different than “teenage” masses or “Italian” mass? That should be self-evident. Being teenaged or Italian is not a disordered temptation.