Yeah, and it's always the same people making absolute concrete sound sense and giving rational debate a good name. (You know who are, bravo.)
If you wanted to challenge it under "freedom of association" you might stand more of a chance, but not over "equal protection". And as it is discussed on this and other threads, some states which permit homosexual sodomy still make a distinction over the the age of consent for adults and minors to have sex.
Some states permit heterosexuals to engage in intercourse, sodomy, what have you at say age 16 (and that includes a partner of age 18+) while holding homosexuals in violation of statutory rape laws for engaging in homosexual sodomy below the age of 18. A "back door" way to throw out the disparity in the age of consent laws, eh?