Mr. York is on track here. Not everyone is as situationally aware as we cyclists (sarcasm intended). Just as in every other context we experience, it is up to each one of us to accommodate those who are less aware. As devilish and hard headed and downright stupid as people can be, what I call "Earth's Adults" are obliged to exercise prudence. Anyway, few of us have a perfect record of safe behavior and most of us have been the beneficiary of other's watchfulness.
All that said, I am truly tested to follow my own advice when I yell “On your left!” and Dim Witted Foot Cattle on the trail ahead leap to their left. They will do that three time out of ten! Sigh.