To me, a marriage has no gender connotations to it. When I think of a marriage, I think of an institution designed for people who wish to spend their lives together (for whatever reason that might be) to declare that attachment publicly. And the idea that marriage, even if it might originally have started as such (Did it? I don't know.), is currently an institution of the church is ludicrous. Heterosexual couples have been able to marry each other and have it recognized as a marriage for a long time even when neither party was Christian.