The P&I clause can cut both ways, since one very important privilege of every citizen is that of local autonomous government, i.e., local self-governance without interference from any branch of the national government (as clearly laid down in the Tenth Amendment). This is probably the central privilege found in the US Constitution belonging to each American. It is, in fact, what the war for independence from England was all about.
This is why I'm conflicted on the issue of the Federal Government claiming supremacy on the question of firearms ownership. The Federal Government, for the most part, was meant to pretty much leave all such matters to local majorities to decide for themselves, by way of their representatives in local government. Could be a camel's nose under the tent deal in the works here.
Would you rather (on any issue) have each locality making its own laws, the result being a checkerboard pattern of different laws across the country, or would you rather have one monolithic set of laws imposed by the Federal Government? In the former situation, if you find yourself out-voted by local (let's say, left wing) majorities, you are still free (worse comes to worst) to pick up and move to some town, county, state, region, where the laws and majority views are more to your liking. Not the case when the central government makes all the laws uniform.
Who's to say that in twenty years, once the Federal Government has made all gun laws monolithic and national in nature, that it will not impose universal restrictions on gun possession that are so onerous that few would be willing or able to jump through all the necessary hoops to bother with them? Where will you move then?
That's why the Founders established our nation as a Federation of, generally speaking, autonomous States (autonomous, for the most part, regarding their internal laws), where the laws under which individual Americans are governed are different depending on where they lived. This way, by hook or by crook, each person was considerably more likely to find himself living under a set of laws he finds agreeable, or at the very least not intolerable.
