Baleur
Prince
This?
I'll risk a theory.
You Mod the MODS (locally) and win every games you log onto forever without any ways for your opponents to track out how you were able to cheat them off fairplay games they trust they could win honestly.
Right?
No, I fail to see how this would be the case. Even if playing with different game files didn't cause the game to go out of sync, there exist countless applications and , most famous of them all PunkBuster and MD5 outputs, which detect this kind of trickery with ease.
Yeah. Also, who the hell CARES about trickery and the risk of cheating going on?
This is not a bank account, its just a game.
Just let us play the game we bought with mods (since vanilla isnt enough) with our friends dammit!!
But no. Oh no. Someone in public games might CHEAT! *ominous music as aragorn walks up to the voice of sauron, barely uttering the word Cheat causes the entire army to shudder in terror*
We better not allow any modding what so ever in multiplayer then, its better to restrict peoples fun than to risk such a horrible fate as 1 random guy cheating in a public game..

There are so many things, so many design choices, i will never understand regarding Civ5..