Laws regarding the legal transfer of firearms don't violate the Second Amendment unless the laws are so onerous as to be proxies for the banning or restriction of ownership or use of firearms.
A ban on the ownership of certain classes of weapons (e.g., semi-autos) is Constitutionally problematic.
A ban on the ability to legally carry a firearm in the public square, let alone in the home, for personal protection, is Constitutionally problematic.
But a requirement that private sales be conducted through the medium of a licensed gun dealer that can conduct a background check for a modest fee strikes me as perfectly legal. Unless, of course, the state imposes so many restrictions on licensed gun dealers so that (as with some states and abortion clinics) there few if any licensed gun dealers are left open in the state.
I've made this point before - when it comes to reasonableness and Constitutionality, the left should view restrictions on guns with the same lens that the right views restrictions on abortion, and vice versa. Can abortion clinics be subject to such stringent regulation that most are effectively shut down? If you say yes, then ponder whether a state can regulate all legal gun dealers out of existence. Because what's good for the goose is good for the gander.