Do you think its better for teens to get the whole truth, or should they be protected?

Today in History, after a long discussion about common misconceptions of Muslims, and tolerance for people in general, my teacher brought in a former student that just came back from Iraq for a question and answer session about his expierience. It turns out he was WAY more honest than the teacher expected and, in between cussing, we ended up hearing detailed descriptions of the people he killed, and how he thinks all Muslims are brainwashed. when asked if he ever read “Three Cups of Tea” he replied he hadn’t and never would. My teacher was so upset about this he came into our next class to apologize for the decision to bring this speaker in. But as it turns out all the kids were really appreciative of someone finally being brutally honest with them, and glad to have heard this.
Whats your take on this? is it better to let (older) kids be exposed and let them make their own decisions with the most information? or should we shelter them until they have better decision making capabilities?