To the Op
Your argument is about as valid as any others I have heard.
I had the same "discussion" with a fomer Marine. His argument, was that Assault weapons are only used to kill people. That no civilian should be allowed to own one.
My argument was that many of the rifles/handguns in use today-originally designed for military use- are now responsibly used by millions of gun owners for target practice, hunting game.
He was not persuaded. Neither was I.