Do you think that the "Stranger Danger" message is taken too far, or do you think that children aren't warned enough?
Sadly, that message doesn't really work very well. The chance that a stranger will do something to
your kid is little, so if you teach your child that the extra safety is minimal. If someone is going around wanting to kill, rape or kidnap children, they will eventually find a child that isn't well educated, so your message doesn't have a global effect either.
And most strangers aren't danger, so you need to be careful not to teach them something that is a lie. Strangers are not to be trusted, but they aren't dangerous yet.
I had these two situations when I was a kid. In one of them, some neighbours were trying to offer me an apple. I was with my parents. I refused, because I was had been taught not to accept anything from strangers. I had to turn down the offer like ten times because they were quite insistent, and finally said that I don't accept apples from bad people and told them to go away. My parents were very upset at what I did, because apparently these neighbours were their friends, and I created such a bad impression about their kid. Well, their intentions were good, they weren't danger, just morons (like most people), but there wasn't any way to know that.
In the other, a person tried to abduct me. He just picked me while I was walking on the street and started to carry me somewhere. Hadn't my parents been around, he might have succeeded. Point is, not talking didn't help, because the person didn't try to talk to me.
So I think that you need to teach your child to be careful, to not trust strangers, but at the same time not to assume malice on their parts. Teach them that some people are bad and dangerous, but most of them aren't. I don't know how you teach a little child something that complicated, because I don't have children of my own.
However, I don't think it's too dangerous if the child doesn't learn it's lesson well enough. It's unlikely that your child will meet someone who is a danger to them. However, you must teach them that such a possibility exists, and they should be careful. Talking is fine, taking rides is not unless the person is a very very close friend to the family, etc. If your child is clever, they'll understand.
During the lessons have in mind that you can't be really sure even in the very close friends of the family either.