Debates about marriage always get bogged down with confusion about religious versus civil marriage. Beck's view that it should be only a religious concept has merit. I see two possible ways to do that. (I’m not suggesting these ideas would ever fly, but we can theorize about them.)
First, we could consider every person as an individual under the law. Marriage would be strictly a religious rite rather than a legal term. The other idea is to have a system for registering couples, just like buying a marriage license, except that no ceremony would be required. All couples, gay or straight, could then be registered as legally joined couples and could have religious marriage ceremonies if they wished.