I worry about this (not about getting shot by my kids, but about coddling them). I'm very much in the camp that parents should instill independence, but there are grey areas.
My oldest graduated from high school last summer, turned 18 in October, and is not in college or working. But he has some pretty debilitating anxiety issues. We've agreed to let him live here with us for a while under some very specific conditions. He must go to therapy consistently and apply what he's learned. He must compensate us for room, board, and car insurance either in money or in labor. At the moment, he makes two meals a week, babysits the two younger kids once or twice a week, is in charge of garbage and recycling, walks the dog, and must do whatever else is asked of him. At this very moment, he's picking up a couple of things at the grocery store for me. He's responsible for his own laundry, dishes, bathroom clean-up (even though it's shared with his little brother), and transportation. I don't buy his clothes, personal items, or special food requests. That's on him. If he wants money, he needs to get a job.
With that all, by the age of 20, he must be 1) earning a paycheck and either out or planning his exit, or 2) in school full-time, in which case he can stay with us until he wants to move to a dorm or rented room.
I used to think I'd be OK with the kids sticking around just so they could save more money. No longer. I want my empty nest, dammit. They can save money somewhere else.