Statistically, strangers are far less dangerous than family, relatives and their adult friends.
The children most at risk are the ones taught from infancy to be absolutely obedient to adults.
As soon as a toddler learns to say "no", he/she needs to start learning the boundaries for themselves and others. If a child feels they have the right to say no and make a big loud fuss about something that feels yukky or weird, the predator won't risk trying to groom them, wouldn't dare go near them.
Teaching kids no to say hello to strangers is as misguided as saying, never pat a strange dog. Better to teach a child how to read a dog's body language and behaviour. Kids can actually read people very well at this level if given the right kind of simple coaching -- they can smell a rat quite well when adults are insincere.
We have to be very direct with children that is all. Say hello to new friends but avoid strangers at certain times. We cannot be blind to how the child thinks.
More proper to teach them to not talk to strangers if the side of their van says... Free Candy
It seems to me that you answered your own question.
Kids can't process information the way adults do. The things kids have to be taught nowadays is incredibly sophisticated compared to a few decades ago. I'd be angry and confused too.If I could figure it out I'd ignore ALL adults