Seriously? What do you expect us to do? Outright ban people off the site for something like this? If we did that, this site would be MUCH smaller than it is. Kicking the person out of 1 is going overboard. There are naive people here that probably didn't read the rules when they joined, and this would also cause a bigger workload for our Administrators (we only have 3), as they are the only ones with powers to do such a thing. They have a big enough workload as it is, they don't need it any bigger. It could also outright make another player lose a game because of it. Example- Player X,Y,Z are left. Player X is leading it, and player Y, relatively new, posts on Z's wall to help weaken him. Suddenly, he's kicked out of the game, and player X has an easier path to victory. Many people in this thread have explained to you how our escalating punishment works. First SD= a warning, second time = 1 week website ban, third time = 1 month, fourth = permaban.
If you clearly think this isn't harsh enough as it is, as people have said, make a Suggestion in the Suggestions forum. I happen to moderate that area. If it garners enough support, I can submit it towards the Webmaster, and he can contemplate whether he wants to implement it or not.
You also have to consider team games (mainly 2v2v2v2). Should the whole team be kicked out, even though only one person asked for the Diplomacy secretly? If not, it also creates Consequences in the game itself, as his partner now receives all of his territories and spoils.