Back in the day I would have been more inclined to do it. Maybe it's just a matter of perception but, generally, I think as a society there is a greater propensity for violence these days than there were when I was younger. Now, like others have said, you don't know who to trust and I mean from both sides of the equation too.
I hitch hiked around some when I was young and have seen that side as well as providing rides. My most discerning moment was when I was 17 and was hitching rides to get home to Tampa from up near Ocala. One fella tried to hit on me. I declined the offer (rather insistantly) and asked him to stop and let me out. He did without issue and I remember thinking about how it could have played out if I had to defend myself. I carried a knife with me when I hitched for just such a reason. Generally though, I never really had any trouble nor gave any.
I really come to think that's it about most things. People seem to have this knack for screwing things up. As idealistic as it may be the world would be a whole lot better place if folks just got along. You give a fella a ride because you're goin that way, you share a little conversation as you go, they get where there going and your trip was a little shorter because of the company, maybe they even give you a buck for some gas. Aint it amazing how we can royally mess up something so simple?
My wife and I have had conversation lately about how I seem to have become more cynical, that I was never like this before. Damn shame I say....