If someone manages to net my drone while I am legally above their property, I will be politely knocking at their door and asking for it back. In the event there is any damage, I will politely ask for the costs to be covered for their negligence.
If (when) they decline, I will serve them a summons to court, along with filing a destruction of property claim with the local PD. They can throw whatever temper tantrum they want, but I'll win, and it'll be costly for them. Just because you don't like something, doesn't mean you get to make up the rules as you go. If you double park in my driveway, it doesn't give me the right to take a baseball bat to your car. And before you cite something like a castle doctrine and that you were "in fear of grave bodily harm", good luck proving that. My burden in civil court isn't proving ANYTHING beyond a reasonable doubt... it's simply a preponderance of the evidence, and if someone has a setup sophisticated enough to bring down my drone at 400ft, they're going to have a heckuva time convincing a judge they were in fear.
The nice thing about our courts is that they (by and large) don't crumble to fear in face of the law. If you illegally damage my drone, I will make you suffer for doing it.
Unless of course, you make me your "friend" by not being a total delta bravo when I show up at your house to recoup my drone (and have you repair any damage you did to it)... which I don't find likely. So basically what I'm saying is: get ready for an expensive legal defense (that you will lose) unless you plan on folding like a cheap suit after you damage my property. It might make for a cool "look at what I did" post on the internets, but it'll be far more fun for me, I promise ;-).