do we always have the choice when we work...?
Yes - you always have a choice, even when you work. However, every choice, whether in aviation or in life, comes with tradeoffs, and some might not like the tradeoffs involved in refusing a flight. I would not have accepted the risks identified for this flight in this thread, however, this choice would be much more difficult if my income/career was on the line.
BTW, my understanding so far is that this flight, while somewhat urgent, was not a matter of immediate life or death. It appears as though the transplant recipient had a substantial time window and continued waiting for a new organ to become available after the flight. As others have pointed out, not an EMS flight responding to a trauma event.