I agree with the point of view that the 2nd Amendment is an individual right, as opposed to a right to arm well regulated militias. The idea was that citizens should be skilled with arms so that when called to serve they would be competent. So no, I don't think SCOTUS was pushing the legal envelope. The liberal Lawrence Tribe has observed that the 2nd Amendment is a pain in the ass amendment, that he wished would go away. I agree with that.
I haven't read Tribe's observations as to the 2nd Amendment, but I will say that the Court has already engaged in judicial activism by creating the standard that they did. The "history and traditions" test goes far beyond originalism. It supplants the text, ideals, and principles of the Constitution for something else entirely. The right-wing is giving the 2nd Amendment a deferential absoluteness that not even the First Amendment has from its most ardent absolutists.
The structure of the 2nd Amendment is unique in the Constitution with just one other exception (the Copyright Clause). The prefatory clause has essentially been read out of the Constitution by those on the right. I think they are wrong to do so. The text is there for a reason and it has meaning. You can read the 2nd Amendment as an individual right without ignoring the prefatory clause. That means that it is an individual right that can be regulated by the government. I think some people get caught up on the word
militia, which meant something quite different than it does today. It's not that meaning has changed per se, just that most people think of militia in the context of the organized militia under the direct control of the government or rogue groups attempting to overthrow the government.
If you consider the 2nd Amendment in the context of the unorganized militia, which was at one point all able-bodied males within a specific age range, it makes better sense. I think it can be read that the Founders intended for the militia to be able-bodied men. That certainly would not comport with today's standards or the Fourteenth Amendment. In that case, it would make sense to read it as the adult citizenry. In that context, well-regulated must mean something more than the government organizing its own forces (i.e. the military and National Guard). The right can be regulated, but not regulated out of existence.
As for the self-defense argument, that is a right that belonged to the people long before 2nd Amendment. Self-defense was and is a right of the people under common law, such as through the castle doctrine.