The second amendment will always be a thing. I can't really comment on what our founding fathers thought, but I wouldn't make that assumption. They had massively powerful firearms that were wildly inaccurate. 200 years of technology has improved accuracy, but not necessarily an individual firearms effectiveness. I'm pretty much in the middle politically, but as you can tell, I'm more gun freedom than gun restriction. I'd agree that mentally ill people should not be allowed to purchase guns without passing through a thorough background check. It might be easier to just ban all diagnosed mentally ill people, but that opens up a world of other issues like banning transgender people from owning guns, speaking of hot topics.

Really the only problem I have with your comment is the last sentence where you said, "Every murderer using a gun was a lawful gun owner until they weren't" which is just so wrong that I don't know where to begin. If you look at all homicides, more than half are suicides and the majority of the remaining homicides are drug related. Surely you aren't saying people don't steal other's guns and commit crimes with them?