Kids can safely experiment with "right" and "wrong" (stealing, murdering, protecting, sacrifice) without permanent marks. You are damaging someone and suffering loss, but you've all opted in. I once leapt into combat to help someone fleeing from a murderer. As soon as I approached, the "victim" drew his weapon. They killed me and divided up my belongings. Real life doesn't offer many chances to try different options in that scenario.
Also, the typical authority structure of growing up (which is age-centric) is reversed. Younger people have less obligations, so generally play more, become more powerful, and end up in the leadership roles. As a 14 year old guild leader you're directing a group of 12 to 50 year olds. I don't know exactly what that does to a person, but my feeling is that it's beneficial.
I haven't really played MMOs in years. I keep an eye on them, and I've been disappointed by the shift to remove antisocial play by adding new game rules and protecting players from loss. It's messing up the risk-reward ratio and removes the chance for social and moral experimentation that was so valuable to me.