Destroying Innocence to Preserve it?

Today was Edens two month shots. I hate shots. I hate them because they hurt and because in my mind, as I hold my child down, in some way I'm betraying their trust in me. I know I'm doing it to protect them, but I can't help but feel angry about having to do so. Every time the nurse stuck a new needle in Eden and her beautiful, blue, little trusting eyes looked up at me, and I saw the pain in them, I wanted to cry while simultaneously punching the nurse in the face. I held back both of these knee jerk reactions so as to not terrify my children, but now that Eden has developed a fever from the shots a part of me wishes I had punched the nurse.

While waiting for Eden to receive her shots we were in the waiting room and Gabriel as always made fast friends with everyone. He is the kinda of kid who doesn't have a shy bone in his body and likes most people. He was truly enamored by one little girl named Charlie and was trying to hug and kiss her the whole time they played together. But that wasn't the only person he hugged, he also ran up to the girls mother and wanted to be held and cuddled, and he hugged the girls grandfather, and wanted up on the girls grandmother's lap. The grandmother thought he was adorable but in no uncertain terms told me how I should not allow him to be so friendly with strangers because he'll be snatched one day. Then went on to berate her husband and daughter every time they interacted with Gabriel.

Now I can see the old bitc..bittys point. But how do I teach a 17 month old to fear strangers when i can barely teach him to not touch the stove? And I guess what I'm really struggling with is whether or not I should. He and I spend all our time together and its not like I let him wander the neighbourhood. I keep a close eye on him because he is still a toddler and needs supervision. So at this age should I be trying to scare the crap out of him and enact the stranger danger code? I mean the only words he can even say at this point are mom, dad, and yes. Should I be trying to add kidnap, molest, and murder to these? Should I be teaching him about bad guys, bad touching, essentially the big, bad world? Should I snatch his naivety away from him already?

When, as a parent, should I be destroying his innocence in order to preserve it? When should I teach him that there is true evil in the world, and that trust should be earned?