What could be the reason some "Christians" favor gay marriage since Christ said God intended marriage to be?

Yet in verse 12 Jesus talks about the 3 types of eunuchs, one (the natural born eunuch) that many believe were gay men. He didn't condemn any of the three types of eunuchs, even though there were shunned by the Jews and not allowed to be taught the Torah. Also note, the first Gentile convert was a eunuch.