What both Oliver Thomas and my mother came up with -separate from each other- is that government should get out of the business of marriage. Government appropriated marriage from religious institutions because it "creates more stable relationships and families, more financial security and a better environment for the rearing of children" -all of which are legitimate concerns, but not religious ones. The thing we call marriage is a civil contract between two parties and the state. Thomas' proposal (and my mother's) is that we merely acknowledge that, call what the state does civil unions, and allow marriages to be overseen by the church. Says Thomas, "Theologically, this puts marriage back were it belongs. Constitutionally, it protects churches from having the government dictate to them which relationships they should or should not sanction."
Thomas has a list of benefits, and -from what I can tell- no real downside. His basis is on the fundamental principle of separation of church and state. It is also about what benefits both the church and state separately. Churches could refuse to perform marriages, couples could find churches that would sanctify their unions, and homosexual civil unions would provide the same stability and financial security to the state that straight unions do. The right of equality under the law would be upheld, as if everyone were getting civil unions there would be no discrimination. He even tackles the "union for procreation" argument, stating that "if procreation were our primary concern, current law wouldn't allow the elderly or the infertile to marry". All in all, I think Thomas has the right idea here. Government shouldn't be in the marriage business; homosexuals should have the same rights and legal protections in their relationships as heterosexuals. Civil unions for all solves those problems; and does so fairly and equitably, if I may say so myself.