I was terrible at Diplomacy when I was a kid. When you're a teenager, your mind is quite likely still struggling with the information that you're learning about the adult world (which is teeming with moral ambiguity) against what you were deliberately taught by adults in the child's world (things like "Don't Lie, Don't Cheat, Don't Steal").
However the sort of ethics that is taught to people in Kindergarten is not meant to serve as your moral beacon through your adult years. It's meant to make you a more manageable child. Once you've outgrown the need for constant supervision, you've also outgrown the need for a child's moral code as well.
Diplomacy is not designed as a contest of intelligence, nor of strategy really either. Diplomacy is not chess. In chess, attempts to distract or harass your opponent are seen as unsportsmanlike. In Diplomacy, attempts to harass or confuse your opponent are the pinnacle of gameplay.
Henry Kissinger is seen as a paragon Diplomacy player because he's intelligent, straight-forward, gentlemanly or honest, but because he's the sort of guy who would volunteer to give your sister a ride to the hospital and then make a point of groping her somewhere along the way.
I'm glad that young people play this game, and have opinions about it, but for many of you Diplomacy can serve as an introduction to the adult world. Underhandedness is everything. People who are both principled and successful are admired by adults because they are so rare. If you give Machiavelli's works a close reading he takes great pain to outline the importance of making personal (and interpersonal, heh) sacrifices to achieve that which is most important.