One loon was really nothing to worry about. However, last fall the U.S. Sportsmen's Alliance (USSA) reported that PETA had acquired drones for the purpose of stalking hunters. With a potentially more organized effort looming, several states are now mulling legislation to expressly ban the use of drones to harass sportsmen. According to USSA, Illinois has already passed a drone prohibition, while Alabama, Tennessee, New Jersey and Hawaii are considering similar laws.
Given that the USSA, NRA and others have already successfully gotten hunter harassment laws passed in all 50 states, I suspect that PETA's plans were already illegal. But it never hurts to give such laws added teeth.
My other question is this: If a private entity—without a warrant, of course—flies a drone over private property, do you not have legal authority to destroy it? I'd consult an attorney before taking such action, of course, but I doubt a $325 PETA drone would be any match for a well-placed load of No. 2 shot.