ATPG, nobody here even used most of those arguments.

Can you give me one good reason why the government should grant legal/tax privileges to two men for living together in a sexual relationship?

At least with heterosexual couples, there were reasons to encourage the development of nuclear families, with the men going to work, the woman taking care of the home/children etc. The family was the basic social unit, not the individual. Of course not every couple would produce children, but there was a general social advantage in promoting the old nuclear family.

But this is history, move on, there's no need to start pretending that homosexual couples ever had such a value. And don't discriminate against single people, the consequences of this discrimination are very real.