I wish more people saw it this way. The fact that a government has any say in who can/can't marry and be with in their private lives is absurd. The concept of marriage should be left up to religious entities.
However, there are many legal matters that are deeply affected by marital status (whether or not you want to call it differently). Many of those rights/benefits are there for good reasons, e.g. child custody, decision-making in medical matters, etc. You can call marriage something different but you'd end up with a legal relationship that looked an awful lot like marriage. Personally, I don't think having a civil union that's different from a religious marriage (with no legal significance) is unreasonable as a concept. But it's not the way institutions have evolved--and, especially now, it doesn't really solve a problem. One could imagine civil unions being expanded as scope but they're never going to be arbitrary so long as there are rights and responsibilities associated with them.
