The *moment* someone finally nuts up at a testing center and throws a Phantom 3 into a commercial jetliner engine, and it does *any* noticeable damage, then we can talk about how easily they will bring down a plane. At this point, with *NO* testing, these assertions come directly from the anal region.
Sensible rules, away from approach paths of airports, and limited to 500 ft outside of those areas, unless licensed to do so. If you can't manage to lift your plane above 500 feet away from the airport, you have problems that 'drones' have no effect over. Christ, planes buzz the 400' tower attached to my work - and the damn thing is painted red and white and blinks, FFS.
Actually, it's the other way round. The way we have brought airplanes from deathtraps to very-very-safe is by testing and estimating risks as much as possible, and avoiding unknown risks whenever possible. You don't tell people "sure, you can do a low level barrel roll with this 747, nobody ever crashed a 747 doing barrel rolls". You tell people "Sorry we have not designed and tested the 747 for low level barrel rolls, so you can't do those with the plane". Jet engines are typically certified for ingestion of birds, water and ice. Not 1.2 kg of metal and plastic. So until we have thrown enough drones into jet engines that we are reasonably certain what drones will and what will not bring down an airliner there are good reasons to be very restrictive.