2A has to apply to states. The wording is not like the other nine. It does not say “Congress shall make no law...”, it says “...shall not be infringed.” It leaves no leeway here. No one within the jurisdiction of the Constitution is allowed to infringe.
Art 6 para 2 is the only “incorperation” any of the Amendments needed. They eventually put in a separate Amendment to try and get it to stick again, but then the SCOTUS screwed that up by coming up with a Selective Incorporation doctrine that is no part of their mandate.