Regarding JB not seeming like he could do this - I'll give you one glaring comparison. Jeffrey Dahmer. In every interview, he was meek, calm, soft spoken, and seemed very gentle and polite. Remind you of anyone? You absolutely CANNOT conclude that someone isn't capable of true evil simply by watching how they act.
That is a silly comparison. JD APPEARED to be meek and calm, but he did have a history beginning when he was what? 10 or 12? JB had absolutely NO history at all! Before, during or since!
If you're going to go by that line of thinking - then Echols is clearly an evil monster based on HIS behavior and words on camera.
Again, there is no history and no proof. WORDS on camera?!? He was a young, "different", outcast teenager, wanting attention in front of the camera. He admitted it himself that he did act like a jerk and a show off (not his exact words). He just wasn't thinking. I do believe this.
You cannot have it both ways. Just like Misskelley being so profoundly stupid and malleable that he was "coerced" into confessing over and over and over again, but this stupidity and malleability evaporates when it comes to someone ON HIS SIDE trying to convince him of something. That is simply not how things work.