People sometimes argue that others — usually conservatives who have expressed some support for federalism — are being inconsistent: How can you argue for leaving topic X to state-level decision, but favor federal authority over topic Y? Such arguments can of course sometimes be apt. But often they seem to me overstated, (1) because they conflate different kinds of criticism of state action, and (2) because they mistake federalism (support for leaving many things at the state level, but deciding many others at the federal level) for a more categorical localism (support for leaving everything at the state level).
1. Let me begin by laying out several different kinds of questions that people can ask about whether something — and especially some matter of ostensible individual right — should be decided at the national level as opposed to the local level. (By local I'll usually mean "state," but similar questions can sometimes arise as to city/county-state relations.)
a. Should the federal Supreme Court protect a certain ostensible right throughout the nation, displacing contrary federal and state decisions? The answer here will often turn on how one reads the Constitutional text. Most federalists acknowledge that there are at least some such rights that are constitutionally protected, but they may legitimately disagree among themselves (and with those who don't much care about constitutional federalism) about which are protected, and how much.
b. Does Congress have the constitutional authority to protect a certain ostensible right by federal statute throughout the nation, displacing contrary state decisions? The answer here will turn on how one reads the grants of federal power in the Constitution, both the Enforcement Clause of the Fourteenth Amendment, and the provisions (especially broader ones, such as the Commerce Clause) of article I, section 8 of the Constitution. (A related question: Should the Commerce Clause be interpreted as presumptively prohibiting states from doing certain things that have an effect on interstate or foreign commerce, absent specific Congressional authorization?)
c. Should Congress exercise its authority to protect a certain ostensible right by federal statute? The answer here may turn on whether you think the claimed right really is morally proper (e.g., Congress shouldn't enact a statute giving parents the right to beat their children, even if it's within Congress's power to do this). It may also turn on whether you think there are practical or democratic theory reasons for resolving certain matters at the state level (e.g., the right solution may be different depending on different local conditions, the right solution will only be reached through state-level experiments, or there are special dangers in federal authority in this area) or at the national level (e.g., the actions of one state will substantially affect behavior in another state, or the claimed right is so morally imperative that we must protect it as broadly as possible).
d. Even if the federal government shouldn't step in, should people nonetheless urge all states to protect a certain ostensible right? One might, for instance, think that states have the constitutional power to restrict guns, punish various sexual practices, engage in religious speech, regulate economic activity in certain ways, and the like — but one might think that such actions improperly interfere with people's moral rights (even if not their federal constitutional rights), or yield various inefficiencies. As to other matters, one might think that states really should do their own thing, especially when one thinks there aren't really genuine claims of moral right involved, or if one thinks that diversity among states is helpful.
It's therefore important, when analyzing someone's arguments for consistency, to understand which argument they're making. There might be inconsistency in arguing for federal constitutional protection for sexual autonomy but arguing that gun rights questions should be left at the state level (though even there one can of course explain why one thinks that the Constitution should be understood as protecting one sort of individual right and not the other). But it's hard to see the inconsistency in arguing that there should be no federal constitutional protection for sexual autonomy (a level (a) argument), but that it's wrong for states to ban handguns (a level (d) argument) and that such handgun ban proposals should therefore be defeated in state legislatures.
2. More broadly, it's important to remember that few people are complete localists in the sense of believing that everything should be done at the local level, or even complete nationalists in the sense of believing that everything should be done at the national level. (Some people believe that federal courts shouldn't enforce any constitutional federalism-based constraints on what the federal government may do, which is to say that the federal government may nationalize all issues, subject only to individual rights objections; but even they don't generally think that the federal government in fact should nationalize all issues.)
Certainly "federalism" has always been understood as a commitment to preserving zones of authority for both the federal government and state governments (and likely partly overlapping zones to boot). At times federalists have stressed federal power more (consider most of the 1780s federalists) and at times state power more (consider most of the modern federalists), but that simply flows from the different issues involved at the time: Federalists arguing against supporters of very broad state power will take the more-federal-power side; federalists arguing against supporters of very broad federal power will take the less-federal-power side.
In fact, today's federalists probably have a broader view of the proper scope of federal power than most of the 1780s federalists had. They just tend to talk more about state power because today they think matters have swung too far in the direction of federal power.
So again one can't just say "If you're such a federalist on the Violence Against Women Act, why are you in favor of national rules governing gun manufacturer liability?" Federalist theory does support national rules in some areas (for instance, regulations of commerce that substantially affect the national economy) and local rules in other areas (for instance, punishment of noncommercial criminal activity).
One can certainly argue that federalists are mistaken about where the line should be drawn, or even inconsistent in drawing that line. But one needs to do that by concretely explaining why the line should be drawn in a particular place, or why two things must in any event be on the same side of the line — one can't just point to the federalist's supporting national solutions in some situations and state solutions in others and say "Aha! Inconsistency!" Federalism is all about supporting national solutions in some situations and state solutions in others. More broadly, I suspect that good judgment, left, right, center, or libertarian is all about supporting national solutions in some situations and state solutions in others.
3. All this may be obvious — but it's the sort of obvious that people miss. Pointing out supposed inconsistencies in others' positions is such fun that people tend to do it a bit too promiscuously. And sometimes, of course, pointing out inconsistencies is helpful: It may help persuade some people that their own philosophies should lead them to a particular result; or it may persuade others that a particular kind of position is inconsistent and thus shouldn't be given credence.
But we need to be careful in allegations of inconsistency (and especially of hypocrisy). Often the inconsistency is more illusory than real, or at least demonstrating it requires a lot more argument than critics actually provide.
UPDATE: My colleague Professor Bainbridge posts his take on a related issue. Quick excerpt: "I am an unabashed proponent of competitive federalism – i.e., the idea that having corporate law regulated at the state level promotes competition between states seeking to attract corporations to incorporate in their state, which competition tends to lead to efficient legal rules. Does this mean I am ideologically constrained to support Spitzer’s crusade even if I think he is more concerned with raising his profile for a widely-predicted future gubernatorial campaign than cleaning up the corporate swamp exposed by Enron et al.? I’ve been puzzling about that question for a while, and have finally concluded I can be a competitive federalist and still want Spitzer to shut down."