Blaming homosexuals for "destroying the institution of marriage" is as ridiculous as the Nazis blaming the Jews for destroying their economy. (And let us not forget that the Nazis targeted homosexuals as well.)
People are looking for someone to blame and instead of addressing the actual problem they look for scapegoats. Homosexuality did not ruin the institution of marriage. If you want someone to blame blame anyone who got married without being fully committed to the other person, blame anyone who got married because it was popular, because they wanted the ring, because they wanted a wedding, because they wanted money, because they wanted status, because they wanted attention or because it seemed like the right thing to do.
Also… about homosexual parenting: If two people who love each other and are committed to each other want to adopt a child, love that child, care for that child… who the hell should have the right to tell them they shouldn’t? That’s one less child sitting in an orphanage waiting for someone to love them. That’s one more child that will grow up in a loving and caring environment. A child growing up living with two parents is a step up from what a lot of children have right now.
In summary: homosexual people are no different than heterosexual people; why don’t we all have the same rights? Our country is not a religious institution and our laws should not discriminate on the basis of religion, gender, age, race, sexual orientation, disabilities, etc..