There is a reason why airports are very, very careful about the vehicles that drive onto runways - FOD (foreign object damage) is a very real thing with very severe consequences when a plane is on approach and take-off.
This often gets mentioned (and is obviously true) but I'm doubtful (but not certain) that it makes that much difference. Things we think about as "soft" can be remarkably hard at high velocity. At 120 mph terminal velocity, water and concrete are similarly fatal: the incompressibility matters more than the hardness.
This isn't to say that drone strikes are not an issue, only that I don't think they are significantly more of an issue than bird strikes. And birds can do a lot of damage at several hundred miles per hour. When you are hit by one, whether it's filled with bones or metal probably isn't the biggest concern.
And yet planes fly through clouds and rain at several hundred mph without issue, though the same wouldn't be said about flying through concrete...
The issue here is relative hardness. Bone is relatively soft to titanium turbine blades, whereas screws and titanium turbine blades are in the same ballpark of hardness, so are catastrophic when they meet when spinning @ several thousand rpm...
1) chucking a chicken bone into an insinkerator vs a penny.
2) a hunk of wood vs a hunk of wood with a nail through a wood chipper.
They shoot a frozen versus thawed chicken out of an air cannon, and conclude that the impact force is identical for both. I'm pretty sure that adding some metal bits inside both chickens wouldn't make much difference.
Density would make a big difference though. A basketball and a 1.75" lead ball have about the same mass, but the lead ball is going to do much more damage. But not because it's harder, but because it's dense and cohesive.
I'd guess that a drone of comparable weight to a goose is going to have a greater impact area, even though some of the internal bits are much harder, and I'd guess this is going to be more important for the level of damage.
Here's an article that supports that view that mass is the main factor: http://spectrum.ieee.org/automaton/robotics/drones/what-migh...
Here's more discussion (which I haven't read yet, and which may well contradict my instinct): http://aviation.stackexchange.com/questions/26223/would-a-dr...
Unlike birds, batteries by definition have a lot of stored chemical energy in them (1). in fact we want to put as much energy in as little weight as possible.
Violent disassembly by jet engine is not going to be a good combination with that.
1) https://www.google.com/search?q=hoverboard+catches+fire
It's possible that such a release could cause a catastrophic failure, but I have a hard time convincing myself that the battery poses a real risk.
Also, larger hobby aircraft (e.g. A 700-size heli) will be using battery packs on the order of 2x packs of 6 cells ("6s" aka 6 3.7v cells in series @4000-5000+ mah), so it's more like ~200-300Wh. Again though, doesn't matter, because even something like a 3s pack @2200mah can make quite a scary fire. This is why there are barrels of salt water at RC flying fields. An overheating lipo goes in the tank before it melts everything with hell fire.
Lipo fires are also why you can't take "hoverboards" on airplanes and why Amazon recalled them all: http://fusion.net/story/250086/airplane-hoverboard-ban-list/
http://www.theverge.com/2016/1/21/10806816/amazon-hoverboard...
Not sure how this is affected by being struck with a blade rotating at tens of thousands of RPMs at hundreds of miles per hour, but my point is that lipos are nasty beyond just their specific energy density :)