there is a constitutional principle called "Reciprocity" which requires all states to accept the licenses and contracts of all other states.
a nevada marriage license is valid in EVERY state, even in states which require far more details before issuing such licenses. by that same principle, hawaii's gay marriages are legal and binding in every state, hence the ongoing flap.
many states do not want gay marriages, yet even one state accepting such unions would compel every other state to accept and honor their licenses. the laws governing marriage (and especially divorce) are complex as fuck, with every state doing it differently. adding a whole new class of "Marriage" is throwing a monkey wrench into the already worn out, rusty and badly damaged gears of Family Law. add in the religious convictions of several prominent faiths (mormons catholics, baptists jehovahs witnesses, 7th day adventists, etc etc etc...) and the whole gay marriage controversy is a trainwreck.
personally i dont give a damn who anyone wants to marry, or how they roll in the bedroom, but when Gay Divorce becomes a thing, thats gonna be hilarious as fuck.