Once again, "traditional" marriage has three features:
1) It is permanent (no divorce)
2) Sexual exclusivity is enforced by the law (adultery is a crime)
3) Children of the wife's body belong to, and are supported by, the husband under penalty of law for default, bastards are the responsibility of the state. (no single mother custody).
Traditional marriage has been outlawed in the United States for at least 50 years. The replacement of traditional marriage with a temporary relation, terminable at will by either party without cause and existing primarily for tax benefits and social esteem, is perfectly suited for homosexuals (in fact, almost all "married" heterosexual couples have a "gay marriage" already).
The foregoing being undisputed, opening "gay marriage for heterosexuals" to its inventors seems inevitable.
Maybe in Sharia law or extreme puritanical situations but traditional views of marriage across most cultures and religions aren't like this. I haven't seen a church (other than Islam) this extreme in years and they are usually fringe, snake-handler types.
even the Puritans had divorce but they had to have good reason, infidelity and infertility were among those