Going with the assumption the dumbest/worse thing will happen:

Cops shoot down an airliner, are granted qualified immunity after proving they were afraid it was a Communist Chinese Iranian drone coming right for them (it was flying away). It soon becomes accepted a certain number of flights will be shot down as the "cost of freedom". A new airline life insurance "industry" pops up selling shoot down insurance at the gate. Swathes of the country are de-facto no-fly zones enforced by various county sheriffs with patriot batteries.

Americans sigh and buy plane tickets anyway. After all, freedom isn't free