well in islam what is condemned about homosexuality, is the act of same sex. that act is what warrants the death penalty. i do not know if islam has a punishment for someone who happens to like the same sex. but like all rules in islam that which leads to sin (crime) is also forbiden. maybe that makes sense?
No, it doesn't, because if homosexuality is legal, then banning same-sex marriage doesn't stop any same-sex sexual acts at all.
What you're really stopping are the things that even Islam (AFAIK) doesn't consider sins. Here's an example of what I'm talking about:
A few years ago, one of my friends suffered a severe (and unexpected) respiratory attack. He was rushed to the hospital by ambulance, where the doctors induced a coma to save his life. He stayed in the coma for a month. Once he emerged from the coma, he was in hospital for another month.
Meanwhile, his wife had to do what she could to keep the family going, but the money she needed to pay the mortgage was in his personal chequing account.
Because they were married, it was a relatively simple matter for her to talk to her bank manager and get access to his account. However, if their relationship didn't have legal status, then she and their two children could've ended up out on the street while her husband was laid up in the hospital, because she wouldn't have had the money to pay for their house.
Now... imagine a similar situation, but where instead of an opposite-sex husband and wife, you had a same-sex couple. Are you really saying that the right thing to do is to have the family evicted?
Where in the Quran does it say that if you disapprove of the sex that two adults have, it's charitable to force their children onto the street?
That's the sort of issue that's at play when we're talking about same-sex marriage. It's not about sexual acts at all.