personally, i've always thought marriage was antiquated and useless. neither a public display nor a piece of paper is going to make anyone do anything differently. being married doesn't automatically make you an ethical person when it comes to relationships. that said, i'm not opposed to getting married, i just wouldn't be the one to initiate the conversation since i don't care either way.
but marriage is very much a legal institution, whether it was influenced by a judeo-christian ethic or not. i mean, most of our laws come from a judeo-christian ethic, we as a country are a judeo-christian society whether you believe in (any) god or not, but we don't see people calling for the abolishment of laws banning murder because they have justifications that don't rely on god's word. so does marriage - there are all sorts of benefits (mostly to the government and not to the people involved) in having people declare where they are and who they're with and requiring them to take responsibilities to take issues off the plate of the government.