Conservatives want to weaken the Constitution to where an individual state can decide that, for examples, women in their state won't have the right to an abortion, blacks in their state won't have the right to patronize businesses that don't want them around, gays won't have the right to marry, and on and on...
Conservatives want all of those without intervention from a Constitution that would otherwise protect those rights.
A weak Constitution is the conservative dream.
And what conservatives fail to understand – among many, many other things – is that the American people residing in the states are first and foremost citizens of the United States, and residents of their respective states subordinate to that.
One does not forfeit his civil liberties merely as a consequence of his state of residence, nor do residents of a given state possess the authority to determine who will or will not have his civil liberties.
When the American people created the Constitution it was their intent to create a National government where the states could not interfere with the relationship between the people and their National government.
When the American people created the Constitution it was their intent to create a National government whose laws were supreme, along with the rulings of Federal courts.
'States' rights' do not supersede the inalienable rights of citizens; the United States is a Constitutional Republic, not a democracy, whose citizens are subject only to the rule of law, not men – as men are incapable of ruling justly; measures repugnant to the Constitution such as Proposition 8 and Utah's Amendment 3 are clear evidence of that.