You make fair points, but it is a bit of a different situation here. Many people here have guns because they think the government will eventually try to take them away from them. Just look at one of the most popular NRA slogans. "I'll give you my gun when you pry it from my cold, dead hands." People take this quite literally. They will fight to the death before giving them up. Yeah, it sounds nuts but I can assure you it would not go peacefully. Would love to be wrong, but I don't think it would go down without a lot of bloodshed.
I agree, the problem would not be solved by the government just banning these weapons, you would see Wacco style massacres going on every single day. It seems that many of these gun fanatics also believe that God gave them guns and he wants them to have the biggest, baddest gun possible. A nutcase with a gun is scary, a religious nutcase with a gun is even scarier. It is of course impossible for a rational, sane person to reconcile these 'God of the Gun' views with the message they pretend to follow in their fantasy religion, but like the small percentage of muslims who become terrorists they twist the words and only listen to the bits they want to hear. The ultimate, original Fake News.
If Sandy Hook did not change their minds, nothing will, the recent Florida shootings in some perverse way just seem to reinforce their beliefs that they are the 'good guys with guns' and they see all these massacres as justification, they need their AR15s because the bad guys have them. Sadly, I don't see a simple answer to the problem and I think a large, influential portion of the USA will continue living in the 18th century and we as a country, will continue to passively support this lunacy. by turning a blind eye.
The rise of facism and right wing hatred in the world is worrying, right wing loonies with guns is more worrying. We see those racist monsters marching in your country, waving swastikas and openly carrying their military grade weapons and your so-called President saying they are 'fine people' - truly unbelievable. We are sickened by the massacres, we cannot even start to understand why a country we used to see as a slightly wayward child who needed to go through adolescence before we saw you as a proper grownup turning into a irredeemable psychopath. There are are of course left wing loonies and they will start arming themselves using the same twisted logic of the right, they need their semi-automatics to protect themselves from the other side. The same mentally disturbed game is going on at a much higher level with your mad leader wanting more nukes than China and Russia, kicking the wasps nest that is North Korea instead of holding out a hand of friendship - yes, Kim Jong Un is almost as mental as Trump, but a bit of ego massaging and good trade deals would work much better than threatening to wipe his country off the map.
As you say, the medicine will be tough to take, but unless you hold your nose and swallow it the USA will become more isolated from the rest of the civilised world, you will become even more hated than you are now. Governments won't act but people will and eventually even the politicians will listen. The boycott movement is growing, it's just a tiny flea bite on the arse of a rogue elephant at the moment, but it will itch and grow into something that cannot be ignored.