I don't think that the Church is actively discriminating against homosexual men, in the same way that it isn't actively discriminating against women by keeping them from being priests. I think the Church is mainly trying to make a stronger statement against homosexuality in a world that is quickly becoming more and more accepting of it. One has to keep a couple of things in mind, the Church isn't kicking gay men out of the priesthood who are already priests, and that if a man were to keep quiet about his sexuality he could still join the seminary. I mean how often do you hear straight priests speak about their sexuality? In the same way if a homosexual priest were to not say anything about his sexuality than there won't be a problem. I can understand both sides of the arguement actually and I guess we'll just have to see how it pans out.

Also I have to point out that this isn't a /doctrine/ of the Church. And it certainly isn't dogma. Certain things have to be set in place for it to be deamed infalliable, in this instance it is simply the Church making a ruling about how to deal with things right now.