Interesting discussion. My two cents.
Going back to the actual 2nd Amendment as written, "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Notice it doesn't say what Arms, just Arms. Notice that there is nothing here that says felons, mentally ill, Radical Islamic Terrorist, and even women!, cannot keep and bear Arms. So when we say that we want to keep those groups from keeping and bearing, we are talking about violating the 2nd Am, as written.
Whether you believe it, don't believe it, like it, or hate it, the Constitution says what the Supreme Court says it says. See Marbury v Madison, 1803. Repeat, the Constitution says what the Supreme Court says it says.
Here is point 1 and 2 in Justice Scalia's majority opinion in Heller (for those who have not read the opinion).
"Held
1.The Second Amendment protects an individual right to possess a firearm unconnected with service in a militia, and to use that arm for traditionally lawful purposes, such as self-defense within the home.
2. Like most rights, the Second Amendment right is not unlimited. It is not a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose: For example, concealed weapons prohibitions have been upheld under the Amendment or state analogues. The Court’s opinion should not be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms. Miller’s holding that the sorts of weapons protected are those “in common use at the time” finds support in the historical tradition of prohibiting the carrying of dangerous and unusual weapons. "
Again, like it or not, that is what the Constitution says (until the Court changes its mind). You see where the Court keeps turning down restrictions on Arms passed into law in some states. For example: "Feb 20, 2018 - In an unsigned order, the court let stand a ruling upholding California's law mandating a 10-day waiting period and another imposing fees on firearm transactions to fund background checks."
Per the Court that California law is Constitutional. This Court is still following the Scalia opinion (stare decisis). And will do so pending a radical change in membership.
If we are going to have an HONEST debate on Arms in this country, we have a long way to go. Both sides are to quick to say that some suggestion on Arms is unconstitutional. Per the Supreme Court there is very little that is unconstitutional. If you just read the Amendment Trump's idea of no sales to mentally ill is unconstitutional. Per Justice Scalia's opinion it is constitutional.