I think it is true that police carry the bulk of the burden for training and the bulk of the responsibility for making things proceed safely. But I think it is unrealistic and ineffective to give them the entire job.

Sort of like, car drivers do have the ultimate responsibility to not hit people, but it sure is a lot safer if we also tell people to generally stay on the sidewalks.

Policemen are generally going to try to do the right thing, but it's a whole lot easier for them to get it right if, in addition to being innocent, you also act safe.