wrong, they attack the person who has the highest bid against themwhich, with the annoying habit of outbidding you 0.0001 seconds before the end of the 'auction' the AI presents, means that yes, he is somewhat right: the pirates always attack the player .
This is what I thought too. But you hear the warning 'intelligence reports a pirate raid is inevitible!' - or something similar. At that point you still have about ten seconds or so to change the target of the raid. In creasing the bid on an AI by about 500 credits more than what is on your head is typically enough to divert the raids towards the poor AI.
In this game that the thread was about I found that out after really babysitting the auction. I made a point of sending the raids towards the AI, and the AI that was raided was then picked apart by me while I faced pretty much no defences. When an AI got some funny ideas I send the pirates after that AI by giving the pirates a mission. I in fact finished the game off by trashing planet after planet myself after the pirates took care of the defending fleet. Then while I crashed player 2, I send the pirates after player 3 again and again. At one point I won a military victory because the pirates cleared the last planet of the AI. At that point I had destroyed maybe 6 planets in total, the pirates cleared all the rest - quite an impressive feat. Needless to say the pirates where nothing short of rediculous in that game.
Now I understand how pirates work, and now I feel like the game is more fun by turning the pirates off. The diplomacy in the game can then unfold normally, and the game folds out into interesting nets of intrige, manipulation and plain fun. With the pirates on this game is just horrible because the player who controls the pirates wins the game. Without pirates the game is actually good and enjoyable.