As a rule whenever the government engages in supposed security related surveillance of citizens its primary purpose is never to safeguard the public but rather to protect itself. It does this so as to maintain its monopoly power over its respective geographical boundaries.
With these drones similar to other security surveillance tools (wire tapping, blimps, interceptions of physical or electronic correspondence etc.) will be used to gather intelligence on anyone they determine a threat to their monopoly power. These threats include regular citizens who are in opposition to their policies or who may have intentions of exposing embarrassing rampant abuses of political power. The surveillance will ultimately be aimed at those this or future regimes wishes to tame, destroy or extort.
In addition one can be sure that the procurement process associated with purchasing these very expensive pieces of equipment will be riddled with corruption as lobbyist representing very "influential" manufacturers bid for these lucrative contracts.
It is noteworthy to mention also that drones carry very sophisticated surveillance equipment, including video and infrared cameras, heat sensors designed for virtually constant spying. They also feature super high resolution "gigapixel" cameras that can monitor up to 65 targets simultaneously from up to 40 kilometres away. They can even eavesdrop on indoor conversations, electronic transmissions, penetrate Wi-Fi networks and intercept text messages and cell phone calls covertly.
The use of such a powerful tool is too tempting not to be abused; especially if it can be leveraged for personal gain. Alternatively it can and will be used to reinforce the user's political power by gathering extensive and intrusive data on any citizen's activities which can then be used in turn to blackmail, extort or or shame accordingly.