The right to vote is a clearly enumerated right in the Constitution. The right to marriage, whether hetero or not, is not. Thus your example is a poor one.
In fact, it seems to me, the whole matter turns upon the question of whether or not there is a Constitutional right to marriage. If not it would be left up to the states. E.g., there is no Constitutional right to drive a car on public roads, and therefore states can have different rules on who is eligible to drive and who is not. I.e., people in the USA can be treated differently for no other reason than the state says so.
Fern
Sorry bud but one correction, left up to the state OR THE PEOPLE.
And I agree, the .gov should not be in the marriage business at all and as far as I can tell has no authority to be in the marriage business in the first place.
Of course the right LOVES "big government" in this case because if the Feds got out of the marriage business gay marriage would be left up to individual churches and whatnot and they damn sure don't want some funny church marrying those funny acting gay folk.