Preferably, that would be campaign mode, but it's not meant to be...
Personally, an option to just turn pirates off would be awesome. As it stands I can never tell if I'm winning because I'm good, or because I always buy off the pirates from the start. I know I could just put my military into eliminating their home world from the start, but I always feel like it would leave me too vulnerable. If diplomacy worked in any reasonable way I could work toward a temporary alliance and launch a join attack to take them down, but in a two player game the AI just won't listen, even if pirates burn their worlds to the ground every ten minutes.
Don't get me wrong, I love the game, but it's these little details that get under my skin and make me wonder "why didn't they fix this?"