Yeah, if the consequences were greater, I wouldn't care. The point is, you can continually drain the AI's money with essentially no consequences in preparation for war. There isn't much I consider a genuine exploit, but this I do. Likewise, I considered ROP rape in Civ3 to be an exploit. If you get open borders and moved a huge army in, you could win the game with the AI being completely unable to compensate. They changed this in Civ4 so you teleport outside their territory if you declare war. It wasn't as realistic, but it was to prevent a huge, unfair advantage. This was even though the AI could technically do the same thing. It wasn't the same in practice, though, just because humans do things on a grander scale that makes it essentially game-breaking.