OK, so now we are beyond the "discrimination" BS, and we are going to discuss the moral aspect. Fine.
Several reasons come to mind why Homosexual/Lesbian sex is "immoral" the first is that the sexual organs of the male/female were not designed for that purpose. For that reason homosexual men use anal sex as a relief, or oral, and many lesbians use a "dildo".
Another one is that neither can bear children, one of the primary reasons for sexual activity. For that reason many fight for adoptions so they can have a "family", and other resort to artificial insemination so they can feel like a woman.
So, aside form the natural reasons, it is also against the commands of the God that created them male, and female, "And Adam knew his wife, and she conceived, and bore Cain". Not Fred knew Tommy, or Sue knew Mary, but "Adam knew Eve his wife"
Then we have Romans 1: 24-27 among many:
"Therefore God gave them over in the sinful desires of their hearts to sexual impurity for the degrading of their bodies with one another. They exchanged the truth about God for a lie, and worshiped and served created things rather than the Creator—who is forever praised. Amen.
Because of this, God gave them over to shameful lusts. Even their women exchanged natural sexual relations for unnatural ones. In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. Men committed shameful acts with other men, and received in themselves the due penalty for their error."
http://factsaboutyouth.com/posts/health-risks-of-the-homosexual-lifestyle/
Have you ever checked into the consequences of their "sins"? "Domestic abuse", syphilis, HIV/AIDS, anal cancer, etc., at rates much higher then those for heterosexuals?