It's almost like that language was inserted into the Constitution for some explicit purpose, but then someone (the Supreme Court) forgot about that along the way...

https://en.wikipedia.org/wiki/District_of_Columbia_v._Heller

I think it's weird how American gun advocates didn't get upset when SCOTUS took some white-out to the amendment they claim to hold so sacred.

Except that's not at all what happened. The plain language of the 2nd amendment is quite clearly and accurately explained by Scalia in Heller. He took no "white out" to it, he explained what anyone without a political agenda has always known the 2nd amendment meant.