A weapon is a tool, killing things is the job that tool was designed to do. No one is arguing different, get your strawman out of here.
Killing things isn’t always immoral or illegal, either. I can hunt wild boar or keep the prairie dog population in check with an AR-15 as long as I have the appropriate licensing and am abiding laws regarding location, etc.
Then there’s the obvious home defense scenario which is unlikely but happens more often than you’d think, the stories just don’t go past local news.