When considering the safety of push-pull, other factors come in to play as well as just 'should the loco lead?' If you had to run the loco round the train at each end of the trip, the turnaround time increases, more infrastructure is required. Both put the costs up. This means that a less frequent service can be afforded, and probably ticket prices increase, so the rail option looks less favorable against bus, or car. We all know that rail is far safer statistically than road, so by not having push-pull you actually make people's journeys more dangerous.
Of course, by having distributed power (EMU/DMU) you don't have a heavier vehicle anywhere in the train so you don't get this 'pushing' issue.
Tim David