I think this is a monumentally stupid idea, for reasons people have already commented on in both threads (and way too many for me to even want to enumerate), but the one aspect I wanted to comment on is how bad of an idea I think it is to even propose this as a serious solution on a major news site.
This idea is authoritarian trash, and it's really not a good look for the people who want changes to the status quo of firearm laws/culture. I mean, I already have a problem with a lot of the ways that people on the left talk about guns, but most of that boils down to ignorance. This idea is straight up totalitarian, and that's really not the kind of thing you want your critics to be able to lobby at you if you want to be taken seriously. Especially when part of the goal of progressiveness (and what I personally like most about it) is the idea that you want to be able to provide people the freedom to do whatever they want (get healthcare, education, live a comfortable life, marry whoever you want, etc.). Forcing someone into military service because they want to own something, especially in a country as likely as this to be involved in active conflict, is downright repugnant to a person that loves individual freedom as much as I do. To me, there's seriously nothing about this proposal that works (even rhetorically - I don't care about calling people out on perceived hypocrisy or whatever, this is dumb idea that looks terrible), and I think, more than anything, it furthers the idea that liberals are a group of people that hate gun owners and want to strip rights from people. As a die-hard leftist that loves guns, it really rubs me the wrong way.
The real solution, as far as I'm concerned, is something we probably don't know yet. The US government hasn't put any research into gun safety in years. Once that happens, we'll probably have a better idea of what will work, and what won't. That, and providing mental health care and coping skills to people who desperately need it.