I posted this in the other thread, but it looks as though the discussion has moved to here.
I was arguably the 'victim' of the sent screenshots - The images published included correspondence firstly between myself and Turkey (in which I made plans to stab Italy with him) and secondly between myself and Russia (in which I made plans to ally with him should his play for a solo fail.)
Initially, I was fairly annoyed that such sensitive messages were sent to the very people I was plotting against. However, I do not actually think it should be banned.
The game is all about getting the upper hand over your rivals. Sending screenshots is one way to achieve that. Yes, it may seem petty or distasteful, but there's plenty that goes on in the game which could be considered those things. Bottom line: if I didn't want other players to know about my plans to stab them, I should have been more careful about who I shared those plans with.
Also, in this instance the player who sent the screenshots did not actually get any kind of advantage from doing so. I was told by Italy that Turkey had sent screenshots. That showed me I couldn't trust Turkey, and so I abandoned my plans for supporting Italy against Turkey and instead did the opposite. By the time the second screenshot was posted, this time in global, the content of the messages caused far less outrage than the actual sharing of the picture which only served to get people's backs up.
No, it shouldn't be banned. If it actually did confer an unfair advantage I'd say it should, but from this example its quite clear that the screenshots didn't help those that sent them in any way, while a simple copy and paste might have done.