A young child knows right from wrong. An eighteen-year-old is an adult, with all the rights of an adult. With rights come responsibilities, one of which is that you suffer the legal consquences of your actions. To cite pop psychology/physiology to excuse criminal behavior by saying "their brains weren't fully developed!" is absurd (and, by the way, moronic). Guess at what age your brain ceases to develop and change? Trick question! It never does, not until you die.

Please, now and forever, stop with the idiotic "their brains aren't developed" excuse.