Currently, pilots cannot open all doors by default on a helicopter without scripting, to reduce clutter in the scroll menu.
However, co-pilots have plenty of attention-space and scroll-space for various functions, such as opening doors. Being able to open doors takes MUCH greater advantage of the "Firing From Vehicles" addition in the Helicopters DLC.
Additionally, this adds more merit to the MI-290's Loadmaster seat, which currently is functionally just a passenger seat.
Making some seats of helicopters, such as passenger seats with the Ghost Hawk, able to be fired from, makes this all the more useful.