With all technology, there is the chance of malfunction - some drones are human operated so human error can also come into this.
At present troops are still the best option until combat machines are tested and don't result in a lot of civilian casualties, however we are looking at Skynet with self aware machines.
I think technology advances like this are good but they should be used with great care - if there are no civilians within a terrorist area - deploy loads of drones.