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.