Why do gay people ask for marriage rights if in the end they won't even get kids ?

People of the LGBT community ask for their right to get married because marriage should be a civil right that is open to EVERY human being regardless of whether they can have children or not. I personally think it’s unfair that straight couples can get married even if they’re infertile, meanwhile gay couples cannot get married regardless of whether or not they want children. Just because people do or don’t want kids doesn’t mean they should or shouldn’t get married. Marriage is nothing but a legal documentation stating the matrimony between two individuals. But it’s also a civil right and should be offered to every human being regardless of their sexual orientation.
As for the question of genetics, I think influence is part of it but definitely not the whole thing. How would you explain kids who grew up being harassed, beaten, and even raped for being gay or lesbian but they still turned out gay when they grew up? If it was influence, then their negative experiences would have taught them otherwise.

What is your psychological reaction to that?