If government had nothing to do with the structure and function of private households, they would treat every one of them in a revenue neutral manner, giving subsidies to none. Then there would be little economic incentive for gays to "marry." Marriage would be confined to the church. If government does allow tax breaks for households, it should treat all of them equally. There could be a head of household and dependents. Dependents could be anyone for whom the head of the household provides financial support, whether it's a spouse, child, sibling, lover, elderly relative, etc. That would be fair.