Some really fine comments. I neither have the time nor knowledge to answer all of them, but let me respond to some that I consider more important.
The evidence is increasing that being raised by a single parent has negative effects on children, although there is debate over how big these effects are. Being raised in an orphanage is obviously not helpful either. I do not know if being raised by same sex parents would be worse than being raised by a single parent, but I believe that it will usually be worse. But one of my main points was that since we allow gays to have children one way or another-increasingly not through adoption- then whether they can call themselves ‚Äúmarried‚Äù seems like a minor consideration.
More than one study shows that breakups among homosexual couples is much greater than among heterosexual couples. Some limited data was included in the first edition of my book A Treatise on the Family, and other studies have been published since then.
Allowing homosexual marriage will discourage some gays or lesbians from entering heterosexual marriages that they later dissolve. But that effect is likely to be very small. If allowing same sex marriage reduced the number of partners among homosexuals, that is likely to reduce the incidence of Aids. That would certainly count as a plus, although I doubt if allowing same sex marriage would reduce turnover of gay relations much more than giving them full and complete access to civil contracts that are fully enforceable in courts.
It is true that informal unions tend to dissolve in very high number, including those among heterosexuals, and in Scandinavia as well as Anglo-Saxon countries. So allowing official ‚Äúmarriage of gays might greatly reduce their turnover rates, but that is still unknown and I believe unlikely.
Some have criticized my claim that children raised by gay couples will tend to be at a disadvantage, partly because they have same sex parents, and partly because they would differ so much from their peers. One person asserts that evidence indicates that diversity is beneficial in schools and other organizations. I believe there is no credible evidence showing that for schools. African-American children, for example, do well in school when they have good teachers, and principals who enforce high and tough standards-just read Thomas Sowell on this subject.
I do not believe it would be difficult to have a civil contract in place of legal and legislative control of marriage and divorce. Most couples would start with a standard form, and only add to that form clauses that deal with special aspects of their relation. I would make such contracts compulsory, partly to remove the bad ‚Äúsignal‚Äù about lack of commitment when a person asks for a contract.