You can't be serious. Shotguns are used for bird hunting all the time and there's plenty "left" to eat, as long as the shooter is at a reasonable distance or 25 yrds to 40 yards. It's not like someone is sticking the dang barrel against the squirrel and pulling the trigger, for crying out loud!
You obviously haven't seen what some of the rapid expanding varmit bullets do on small critters out of the .223, Simply devastating!

If ya need a reason to buy an AR, find a better one than to shoot squirrels out of trees with. The shotgun is a much more intelligent tool for the job!