It's one thing for governments, who have some legitimacy in what they're doing, but have other people doing it... it's not going to happen."
I completely disagree. They have no legitimacy to be doing it whatsoever. Private individuals actually would, whether for resource prospecting, security, or search and rescue. There's lots of legitimate commercial applications for it. But letting a completely unaccountable, monopolistic organization that has the power to imprison and/or fine you thousands of dollars for destroying their hardware? Letting them monitor, track, and pass judgments upon you remotely from hundreds of feet in the air?
You must think CISPA is fantastic.
If a espionage drone is flying over my property spying on me, I should be allowed to shoot it down, whether or not it's from the Government.
That would be the answer. If people didn't have the skills or capabilities to defend themselves from private property drones I am sure the free market would think of solutions. Some companies might do it just for salvage rights.
Due to people shooting them down or disabling them by other means, I believe their deployment by private individuals would be cost-prohibitive outside of business applications. I think common law would largely recognize people's right to protect their privacy from such drones. Seriously, who could blame someone for shooting down a drone that was monitoring them? I believe we call that "stalking".