and you keep missing my point...that vector introduced through rotation will change as the crew moves about the ship...No these little minute seemingly insignifigant forces at work won't instantly change the ships vector, but over time they will...And for short distances these changes don't amount to much...but for long distances it sure as hell does
But this wouldn't be a problem if there were enough fuel onboard to perform course corrections mid flight (just like you would have to do with any ship)...but the big remaining problem for such rotateing sections is mechanical in nature, specificly the bearings and seals around the pivot point (eventualy the fricton generated by these moveing parts will effect the rotation speed...so more energy will need to be spent to compensate, cause if those rotateing sections are not spinning fast enough to counter each other then they arn't helping to maintain the flight vector...needless to say that trying to maintain or even repair such bearings mid flight could be a real chore)...The KISS (Keep It Simple Stupid) principal should never be forgotten...keep the ship in zero G, keep enough fuel on hand for flight path corrections, and provide rotateing beds for the crew to sleep in (that way if the bearings in the bed need repaired, the whole ship isn't at risk of comeing appart) the rotateing beds should simulate enough gravity that it keeps thier muscles from signifigantly weakening and heart working properly...
in a way your both right. i can see it if you dont have a counter rotation section teh ship might waste tons of fuel keeping the non rotation section from rotating. from all the designs i seen that use rotating living areas that the mass would be so large they would spin the nonrotating section instead of the intended purpose.