Transponders are not required for payloads below approximately 100x the weight of these types of balloons. There is zero liability, but also zero recourse.
It's hard to argue that if the government can't identify something operating in controlled airspace that it can't take measures pretty solidly in the realm of "national defense," up to and including blowing it up.
It's hard to argue that if the government can't identify something operating in controlled airspace that it can't take measures pretty solidly in the realm of "national defense," up to and including blowing it up.