Almost everyone would drive the bulldozer. For the vast majority of the population there is almost nothing that they are willing to die for.
I forget some of the details, but I've heard of an experiment done where there is a man in a room who is supposed to be doing a task and a person on the outside who can see in has a knob. If they turn the knob it administers an electric shock to the person and they are supposed to make them do things or get shocked. There is a person standing there telling them when to turn the knob and after the person failed to do as instructed a certain number of times the person in authority would instruct them to turn the knob up another notch, that notch being marked as "FATAL". Supposedly almost everyone turned the knob to fatal and threw the switch.
Now it is probably true that if you were to interview these people none of them would have said that they would do that.