Apparently you've never had a plastic bag break dumping your groceries on the ground. Try chasing rolling bottles of pop going under cars when it's below zero out. Never had that happen with a paper bag.

I've had both break. Plastic bags tear when overloaded or structurally unsound. Previously sound paper bags become structurally unsound when soaked, and it doesn't take much wet to soak them. (And unhelpfully, the things that could make a paper bag waterproof also make it non biodegradable).