In general (not a complete answer for point impacts) a pressurized fuelage is much happier if it deflects as smoothly as a baloon. So if you start cutting holes in it you are going to have to add material to force the fuselage not to kink around those big holes. This typically adds stiffness against inward buckling as well.
Take a gander at crashed planes in the R&N threads and you will see that the door locations are the last to buckle and break the fuselage.
For point impacts, the fuselage skin is the defence and that tends to be similar thickness over the pressurized areas.