Well, there really *are* advantages to regularizing state regulations, some of which are quite attractive to many conservatives. One example that comes to mind is the attempt regularize state firearms regulation so that it is practical to (for example) transport a firearm between Indiana and Iowa across Illinois - which has more restrictive firearms regulation than either of its neighboring states.
We wouldn’t have that problem the you mentioned if all states obeyed the 2nd Amendment and repealed their gun laws.
My congressman is Mark Kirk, an Illinois Republican who is pro-choice, pro-gun control, pro-gay marriage, pro-illegal alien, pro-spending increases, and anti-Iraq surge. He said that he opposes congressional earmarks, but he ensured that the federal government spent money, in our district, for Headstart, commuter trains, and local police depts. I emailed him and reminded him about the 10th Amendment. I said, “Please write to me and tell which articles, of the Constitution, mention education, trains, and police departments, or tell why you support disobeying the Constitution.” I didn’t receive a response.