A) If schools are supposed to promote Evolutionary theory, and that each individual human will do whatever is in his interests to ensure survival of himself, his family lineage, his town, and his species; then PROMOTING gay marriage as a realistic lifetime partnership counters that theory about why humans exist. However, maybe Humans are touched by God, and the laws of Evolution don't apply to humans since we were created by God and not connected to the animals on this planet. A Government has an survival interest in promoting procreation because more children mean more taxes paid, more children to farm, more children to support senior citizens, and basically survival of the human species. A Government does not need to encourage or support something that does not contribute to its function.
Evolution is scientific fact, just like Newtonian physics (with relativistic qualifications), the gas laws, and the atomic theory of matter. Science has no moral lessons to teach. Science can tell one the effects of giving a cyanide pellet to a victim; morality tells one not to commit murder.
It is possible to have an atheist marriage. Think of this: no Commie state, however militant its official atheism, ever outlawed marriage. The rest says much about your prurient interest in sex.
By the way -- many marriages are done in which there is no possibility of any pregnancy, In fact there is much sex that can never result in a child. Do you have problems with marriages involving the elderly, let alone elder sex?
Marriage has values other than legal formalities.
In view of AIDS, promiscuity among gays has become a dangerous habit. Lesbians seem to have very low rates of AIDS. But let us remember -- few jurisdictions have decided that marriage is a good way of promoting monogamy.
Bullhist! Birth control can lead to more sex and hence a stronger personal bond within a couple.
Marital infidelity can wreck a marriage. But I have seen other causes, like spousal abuse and "mental cruelty". Some marriages are mistakes from the start, which relates heavily to people getting married in their teens. I have known this one:
"We are having financial problems and you are spending money on... a boat? a motorcycle? camping gear? an expensive hobby? expensive jewelry? You ask me to make sacrifices, yet you can't think of anything more than that damned piano?