"A plane may land damaged but it WILL land. A drone going through the engine will probably cause less problems than a bird"
The issue here is with the word "probably". You and I are sitting at home, glass in hand, browsing the interwebs, Would you feel as confident if your family were sat in a 767 on finals with a drone directly in the glide path? It's also not just about approach, but departure.... aircraft can't takeoff if there's a risk of something popping up just as it reaches Vr; bad things happen. As for missile defence systems.... dream on. Unless the Pk is 100% you've got the potential of a f*ckton of collateral damage to cope with.
Much as I enjoy a good conspiracy theory, I'd also like to point out that 1902hrs GMT tomorrow (21 December) marks the 30th anniversary of PanAm 103 exploding over Lockerbie. with the loss of 270 lives. I don't want to see the same again. This is peoples' lives we're dealing with... show some fcsking humanity ffs.