Chuks, you are correct, if you are taxiing or parked with engine running and you see a risk to someones life of course you are obliged to save that persons life if you can. If you didn't take action, I very much doubt you would be charged with murder as the gyro pilot has been though.
If on the other hand, some angry person runs out in front of your aircraft and you fear for you own life/safety why should you stop the aircraft?
Edit:
From the UK ANO, section 146...
"Obstruction of persons
A person shall not intentionally obstruct or impede any person acting in the exercise of his powers or the performance of his duties under this Order."
Last edited by Cabin doors 2 manual; 10th March 2009 at 21:29.