The Supremacy Clause of the U.S. Constitution says that federal law supercedes conflicting state law. In addition, most rights contained in the Bill of Rights, protected under the U.S. Constitution, may not be infringed by the states. It didn't use to be that way, but it is now.
Voting laws were, and are, left up to each state. The federal government has no power over those laws. If the states required a literacy test or a poll tax, if they excluded non-whites, women, those under 21, etc., they were free to do so. Amendments to the U.S. Constitution changed that, and the 14th amendment made those rights applicable to the states.
The second amendment has not yet been "incorporated" and made applicable to the states (neither has the third amendment, the grand jury indictment clause of the fifth amendment, and the seventh amendment).
Therefore, the second amendment only applies to gun laws written by the federal government, not the states. In other words, the federal government may not violate the second amendment. States can.
If the U.S. Supreme Court reviews Parker and decides that the second amendment does not protect an individual right, only the residents of Washington D.C. are affected -- the federal law only covers the residents of Washington, D.C. No state laws would be affected by this decision (since, again, the second amendment doesn't apply to state law).
What would happen is that state legislatures would look at the U.S. Supreme Court decision and use that as leverage to pass more restrictive state laws. Of course there's no connection, but liberal legislators will make one.
Now, states may always write laws that are more protective of rights than the federal government. Unless, of course, those rights conflict with rights held by others.
You seem to be of the opinion that the Constitution and the Bill of Rights means whatever the courts say that it means. From a practical standpoint, we are stuck with their decisions. But that does not make them right or wrong in any given case.
Since the Supreme Court has been silent with respect to "incorporation", we do not benefit from such. But it cannot be that the meaning of the Constitution is like some political quantum physical experiment, where we can't know the proper outcome until the court rules.
At such time as the Supreme Court "incorporates" the Second Amendment, that will be their decision regarding what the Constitution has meant since the passing of the Fourteenth Amendment.
So you are free to tell us what you think they SHOULD DO. If they "incorporate" the Second Amendment does that mean that YOU were wrong concerning the meaning of the Second? Or does that mean the Supreme Court is wrong in "incorporating"?