I think we should focus on low hanging fruit first. Until our politicians focus on quickly and easily eliminating a huge amount of gun murders by ending the war on drugs, I find it hard to believe that their goal is to eliminate a huge amount of gun murders.
As for the harms caused, I am trying to think long-term outcomes. I often hear that nobody wants to take away my guns and that an assault rifle ban would be for future purchases. Assault rifles only account for about 100-150 murders per year, most of which would still happen with an alternative weapon. The people proposing this KNOW it will not register as anything more than a rounding error on the stats. Do you really think a significant portion of people who are screaming about stats and calling for assault rifle bans will be like "whelp, we tried...whatevs" when the numbers don't change?
My bet is no, they'd look for the next ban. And then the next because that didn't work. Eventually you ARE left with confiscation.
And what then? How do you confiscate 300,000,000 guns? With force? What kind of force? Are you OK with sending 10,000,000 people to prison if they don't give up their guns? Are you OK with tens of thousands of swat raids per year to try and get the guns from people? What about the swat members or gun owners killed in these raids?
What do you think we should do and why should it not begin with ending the war on drugs?
The trend seems to be for more-and-more guns owned by fewer-and-fewer people. Plus for ever-larger spree-killer bodycounts. (Though it's true that such mass killing incidents only make up a small proportion of gun-deaths, they do focus the public mind). Eventually it will be one guy owning several million guns, and arresting him won't be as hard as arresting a few million people with one gun each.
Being serious, I do believe demographic change (not just racial demographics, but urbanization and increasing education) is going to eventually change attitudes, but it's going to take quite a long time and a big pile of bodies.
Also, the evidence seems to be that the critical driver of the US love of guns is its history of racial politics, or, more crudely, racism. Race has poisoned everything in the US. Europe is only now starting to experience race as a domestic issue to the same degree, and, while there's no 'moral' difference (that is, I wouldn't claim European white people were 'less racist' in any possible sense - quite the reverse, if anything), I don't think it's ever going to be the same in its effects because it lacks that very specific long traumatic history.
For Europe racism has traditionally had its effect as a foreign-policy issue, as a driver of imperialism. We feared and exploited non-white people overseas rather than at home. So personal gun ownership didn't really come into it.
Actually, for the UK, feels as if that 'non-white' category was quite an expansive one, including much of Europe itself.