1. We have to restrict marriage to opposite sex couples because we need to encourage procreation, which is "essential to the survival of the human race."
2. Homosexuality is not an immutable characteristic; therefore, homosexuals are not a protected class, which means it is OK to restrict their rights.
3. Marriage is not a fundamental right because there is no history or tradition of same-sex marriage in this country. As regards miscegenation laws, those were only a burden upon opposite sex mixed raced couples; therefore, that experience does not apply here. Ultimately, it's all about procreation: anything that gets in the way of procreation between any two (opposite sex) humans is a violation of a fundamental right, but not this.
4. Discrimination only exists against the politically powerless. Because homosexuals have been able to gain some legal protections in the past, they are not powerless, ergo any rights they may not have now they can win through the political process.
5. It is not the court's role to restrict the state legislature's decisions, regardless of the logic given behind their legislation. For example, the state legislature is welcome to restrict marriage rights to opposite sex couples based on simple prejudice; because they feel that children "thrive" in households with one parent of each gender, there is nothing wrong with restricting marriage on that basis. There need not be scientific proof that this is a correct view, only belief.
6. There is no gender discrimination here because everyone is free to marry anyone they choose (of the opposite sex).
7. Remember, DOMA is about encouraging procreation, so it's OK. (Thanks, Clinton.)
8. Because plaintiffs expressly requested that the court not consider whether denial of statutory rights and obligations to same-sex couples that apply to married couples violates the state or federal constitution, we didn't talk about that at all, even though maybe (kinda sorta) they might have done better if they'd mentioned that stuff instead.
9. Just because the sterile, elderly, infertile, etc. are allowed to marry doesn't mean that that has anything to do with legislative intentionality - it's OK to restrict marriage in order to promote procreation even though many who marry cannot procreate. The intent is enough, no matter how absurd its implications.
10. Ultimately, it's all about furthering the state's interests. Because furthering the state's interests is paramount, no matter whether or not those interests are legitimate (they can be based solely on vague ideas such as "having children is good") or even rational, equality under the law or simple fairness is not important. Yes, there may be more just and human ways to further the state's interests - we admit that these laws are grossly unfair to some of our citizenry - but that's not for the courts to decide, but rather the state legislature.