Banks has the advantage of being flip when explaining anything, so none of his explanations really need to hold much water. If you "need to ask a Mind" it just elevates the question to the next level (and the whole idea of Culture percentage, or however it's put, indicating almost any Mind is really only partially conformant to the mainstream, is a huge loophole -- what stops the Culture from becoming the hegemonizing swarm from Hell? It comes down to an argument about what sentient beings will do with unlimited power).

Banks at least has put enough thought into it to give flip answers, though. Star Trek is a mindless mess.