The harm to humanity is two-fold:
1. Most importantly it brings humanity into God's wrath.
2.If the homosexual lifestyle were to prevail, the natural order of our species becomes exitinct and only a veiled attempt at "regeneration" of a soul-less race would continue. (should God allow it).
How can homosexuals believe that what they're doing somehow is a natural tendency? If it were so why are male and female born with different but complimentary genitalia?
I've heard it said that God made homosexuals. This is not true. Homosexuals make homosexuals. No matter how you feel about your sexuality. Love does not equate to sex. I had many same sex friends I loved and never had sexual attraction to them. To have sexual attraction to the same sex is unnatural. Psychologists have only served to confuse the general poplulation on this issue for decades.