[Trapped Behind Enemy Lines]

As I understand the Constitution, states are pretty much free to do whatever they want, unless it is specifically prohibited by the Constitution. States regulate issues such as marriage, abortion, automobile because they are not covered by the Constitution. States even have the power and authority to set up an official state religion (the federal government cannot of course) if they so wanted to.

[Olog-hai]

The Tenth Amendment is not a free-for-all.

And governments that contravene the model of a republican form are specifically prohibited by the Constitution.

[Steve_Seattle]

"As I understand the Constitution, states are pretty much free to do whatever they want, unless it is specifically prohibited by the Constitution. States regulate issues such as marriage, abortion, automobile because they are not covered by the Constitution. States even have the power and authority to set up an official state religion (the federal government cannot of course) if they so wanted to."

That is correct. Even Robert Bork conceded that the Constitution does not prohibit the states from passing bad laws, and the Constitutional limits on the states are relatively few.