to go off on a tangent then (if we hadn't already), do you think that it is impossible for atheists to be truly married - and by extension, do you think the same of people who have different faiths than your own? how about atheistic religions such as buddhism? none of the afore mentioned marriages involve a relationship with god - well at least, not your god.
the word "marriage" does not belong to christianity, and christians have no right to say who can and can not get married.
that said, if a religion does not believe in gay marriage, then obviously no gay couple can demand it's blessing.