Thomas,
You are correct that the airplane does not care, but the people do. The FAA has made clear in the case of class B HEC just as public use that risk is relative.
Essentially, it is too much risk to expose paying passengers for hire unbeknownst to them, but not so dangerous as to disallow trained persons who accept the risk in the course of an effort to perform such critical duties.
Give it the common sense test. Is it realistic to pull firefighters out of the northern california forrests without entering the HV curve, Nope. The only thing they could have done differently in that regard is limit the aircraft to 9 seats.