There are plenty of gays who argue against gay marriage and a vociferous number who are for it. It's called debate. Some against argue that gay marriage is homophobic.
http://blogs.spectator.co.uk/coffeehouse/2013/02/same-sex-ma...
(Might be paywalled but the arguments can be found elsewhere on the web - though I would not expect you to search for them.)
"We have profound reservations about same sex marriage not just because of the harm it does to a vital heterosexual institution but also because we reject the implication that in order to be equal and respected homosexuals should conform to heterosexual norms and be in effect the same as heterosexuals. In this sense we believe same sex marriage to be homophobic – it demands recognition for gay relationships but at the price of submitting those relationships to heterosexual definition. This serves neither homosexuals nor heterosexuals."