Re: 500g Drone vs 100 ton airliner
Of course a drone isn't going to immediately outright "destroy" a plane. No one's claiming that. But it will be bad news to an engine if ingested. Or a windshield. It'll be expensive, and the airport doesn't want to be on the hook for the potential repair bill, the airline doesn't want to deal with the insurance and downtime, and of course, there's the safety aspect.
Other posters are sharing scientific studies. Here's an unscientific one - a bird going into an engine:
Now imagine a metal and plastic drone, of unknown size, with a Li-on battery.