1) The government should just get out of the marriage business altogether. As far as the government goes (all of them, state, feds and city hall), there should only be civil unions. These would be for the purpose of sharing various burdens and expenses. Your civil unitee could file a joint tax return with you, share your employer-sponsered health care, collect death benefits on your demise, automatically inherit your shit, etc., etc. You get to choose one person to have a civil union with at a time. It can be your opposite sex spouse, or your same sex spouse or your 96 year-old uncle who will need the proceeds from your estate for assisted living if you get run over by a bus. Whatever works for any two people who can agree to be domestic partners. Then if you are a rabid religious fanatic, you can have a genuine Sanctioned-By-Jesus straight marriage that is licensed, performed and recognized by your particular church which, if you wish, can be the religious arm of the Flat Earth Society. Or you can have no "marriage" as such at all. Or anything in between.
Under this plan the government does not say who can or cannot be partners. Any two people over eighteen years of age can be civil unitees. They have to remain aware, however, that having entered into this share-your-shit agreement, you're going to have to hire a lawyer to get you out of it--just like a divorce. Just because it's a different, more equitable, less discriminatory setup, doesn't mean it can be loose one. You're still responsible for kids you create, debts you run up, promises you make or break, etc., etc.
Let churches decide who's married and who's not and let each of us decide on which church we wish or wish not to attend. If your church doesn't recognize your particular marital stripes, then go start a church of your own that does. You can start a church that does not recognize marriages between people who wear white shoes after labor day if you want, and--within the confines of your church--you can enforce that rule with an iron fist and anyone who doesn't believe as you do can just go eat boogers!