Garbage Collection Drones Pros and Cons

It's a mad idea. so here are the pro's and cons and possible implementations:

Cons:

Drone cannot carry as much as a robot boat and a robot car
Convicts are supposed to do that kind of thing
Development cost currently in the tens of millions including recharge station
Drones aren't robust and require maintenance
Drones can't navigate green areas reliably except for lawns
Liable to theft
Small distance of travel, i.e. 500m from recharge station
Daily rubbish collected in the order of 20-300 food packets
Disturbs the peace, people walking don't want too many robots in the air
Brings to mind visions of 100ds of autonomous drones for every purpose filling the skies and potentially being used for spying and then for police and army use.

Pros:

Faster than land travel.
At work from dawn till dusk.
Can deal with alot of small litter
Can clear a beach automatically
Could perhaps bring in 2000 food packets and bottles every week

Conclusion: 

perhaps in a theft free zone, a solar panel with a couple of drones on it could clear up a perimiter of 500 meters slower than a human could.

Amphibious boats would be much more reliable for canals and rivers, to stop all the plastic arriving in the sea, and 5 of them could possible stop all the rubbish floating downards from a city into the sea.