From The Federalist:

On its face, this law clearly violates the spirit of the Second Amendment. Conservatives arguing to overturn it, however, find themselves in the awkward position of arguing against long-standing conservative principles like constitutional federalism and state sovereignty. Implicitly, in this case, the argument for gun rights relies on a century of progressive precedent known as the “incorporation doctrine.”

Activist courts have used this legal theory to impose left-wing policies top-down onto the states. Conservatives are right to insist on a consistent standard; if the Constitution means no school prayer in Kansas, then it also means the right to carry a gun in New York City.