I think you are missing the point.

First throw out the FAI part of this argument; we can consider an FAI just as a tool to help us achieve our goals. Any AI which does not do at least this this is insufficiently friendly (and thus counts as a paperclipper, possibly).

Thus, the actual question is what are our goals? I don't know about you, but I value understanding and exploration. If you value pleasure, good! Have fun being a wirehead.

It comes down to the fact that a world where everyone is a wirehead is not valued by me or probably by many people. Even though this world would maximize pleasure, it wouldn't maximize utility of people designing the world (I think this is the util/hedon distinction, but I am not sure). If we don't value that world, why should we create it, even if we would value after we create it?