Imagine a game with all trustworthy players. Germany and England (England and France or Germany and France) make an alliance, but neither can lie to France (Germany or England), so they either don't talk with him or they tell him the truth. In this case France is most likely overpowered by two countries. There's not much point to talking to your enemies, cause they wouldn't betray each other. And there's no information to gather cause you already know the alliances.
You could also take that to another level, if two players are losing to two other players, and one of them is substantially more powerful, then no one could beat him. You can't convince his lesser ally to betray him.
This just seems dull and too simple. There would be so little communication because players would lose one of their greatest allies, reason and logic in a discussion.
I suppose you might hope that you just have one player that would be trustworthy and all the others have their own ways of playing. If you play that way, then your essentially meta-gaming (you have one ally that won't betray you under any condition, is that fair?), which then might result in everyone else teaming up on you.
I used to think in similar manners back when Risk was my favorite game. I thought that if you wanted a game of players that would not betray each other, you could not have alliances, because eventually someone would be betrayed in a FFA game (except for my few friends who thought it was funny to declare world peace). I thought this gave me an advantage because I had superior strategic planning, and in a game without alliances, strategy is everything. I was basically arguing a useless point, because alliances and betrayal are also important in Risk. I was just trying to argue a point that would help me just like your point would help you. Granted my forceful personality when playing risk, forced everyone to loosely follow my rules.
Anyway, this past December, I discovered Diplomacy, and my mind was blown away.