"do as mummy says" or "do as daddy says" isn't actually 100% safe either: parents do abuse children, parents do make wrong or dangerous decisions regarding their children
but it is safer on balance- most of us are not abusers, and most of us make wise and sensible decisions most of the time
as our children grow we start leaving their safety and wellbeing, and the safety and wellbeing of other children around them, in the hands of other adults- teachers, childminders, the people who run after-school clubs, swimming instructors, bus drivers
of course we should teach them specific safety advice, e,g, about private body parts and not getting into somebody's car
but if they don't have the general attitude that they have to do as they are told by the teacher/TA/caretaker, then they won't be very safe at school and they could well pose a danger to other children around them
and those attitudes are likely to linger: a child whose main attitude towards the primary school staff was one of suspicion and I-don't-have-to-do-as-you-tell-me isn't likely to sit down and stop clowning about when told so by the driver of the school bus in secondary either