since gay people are all individuals, they have the same constitutional rights as all other individuals in the USA. This includes marriage, adoption, whatever. Its individual rights, not gay rights, black rights, women's rights, etc.
The thing about that is... marriage, adoption, even sex and procreation are technically not Constitutional rights, whether you're gay or straight. This is decided by the state level, which is something Ron Paul clearly endorses.
Consider the Lawrence case decided by the Supreme Court last June. The Court determined that Texas has no right to establish its own standards for private sexual conduct, because these laws violated the court’s interpretation of the 14th Amendment. Regardless of the advisability of such laws, the Constitution does not give the federal government authority to overturn these laws. Under the Tenth Amendment, the state of Texas has the authority to pass laws concerning social matters, using its own local standards, without federal interference. But rather than adhering to the Constitution and declining jurisdiction over a state matter, the Court decided to stretch the “right to privacy” to justify imposing the justices’ vision on the people of Texas.
- Ron Paul, 2004
For those who are not aware of
Lawrence v Texas, it was a supreme court case in 2003 which struck down all sodomy laws which applied only to same sex couples. The Texas law prohibited oral and anal sex, which in Texas is legal for straight couples. I don't think I'm spinning the issue at all when I conclude that in Texas it was illegal to be gay and Ron Paul considered such a law to be Constitutional.
You might find this example absurd, but if Wyoming instituted population control -- one birth per woman and no more -- I'm pretty sure it would be Constitutionally permissible. Remember that the Constitution is a legal document, not an arbiter of justice with implied jurisdiction over the unfair. If your rights are not explicitly protected, the states can walk all over them.
After all, in Virginia it's a felony for an unmarried couple to live together. In Alabama, it is illegal for a man to seduce "a chaste woman by means of temptation, deception, arts, flattery or a promise of marriage." In Arkansas, adultery is punishable by a 20$ - 100$ fine. I could go on.
There is pretty much no Constitutional limit to how intrusive a state government can become in most matters -- marriage, adoption, whatever. And states are very much permitted to pass separate laws for gay and straight citizens.