Air Carrier pilot questions the wisdom and legality of bleeds-off takeoffs in the A320 series aircraft.

Narrative

I am not sure that we have the justification from Airbus to perform unpressurized takeoffs. In the Boeing; we used to take off with the engine bleeds off and the APU supplying pressurizing air; and I was of the belief that this PSID was applied for structural rigidity reasons - about .25 PSID; if memory serves. Now; we are blasting down the runway with flaps 1 and speeds into the 160's with a flaccid; unpressurized airframe; wreaking God knows what kind of damage to the airframe with the high vibration and 'soft' fuselage. These speeds themselves seem ridiculous given the fact that other operators are performing routinely the takeoff's that we consider unusual (Flaps 3 with speeds less than 'paint-peeling'). We've gone so fast and set up such strong vibrations in the plane that we have knocked off-line IRU's and kicked the plane into Alternate Law at takeoff! FOM II 7.20 gives guidance for unpressurized flight; but it is clear from the charts that this is performance info to be utilized in the case of a Rapid Depressurization and subsequent high dive to 10000 ft. It is my humble belief that we do not have any Airbus-approved data or basis or waver or authorization to conduct unpressurized takeoff's ; and I believe that every takeoff we conduct amounts to test pilot work. If this data/basis/waver/authorization exists; I would like to be privy to it; as I have my doubt as to the legitimacy of the procedure; based upon the sum of my (and the last FAA jumpseater's) knowledge. If I am wrong; I will be the first to say sorry for the inconvenience; but I am fairly certain that this ill-conceived policy was enacted during a time when fuel prices were making management pull out what little hair they had; but now; in saner times; we must analyze whether what we have wrought may be our (structural) undoing.Provide data to the pilot group to confirm that an unpressurized no-pack takeoff is an acceptable procedure. Maximize lower-speed; higher-flap-setting takeoff's to reduce vibration and structural fatigue. Granted; these two issues are separately resolvable; yet they are fundamentally linked and negatively synergistic; hence; the attempt to report both at the same time.