It would be GREAT if you could interact with objects in mouselook while you have a gun attached.
Holding alt doesn't work; you have to detach your gun first. If ALT could suspend granted permissions, or some other keystroke or whatever, that would fit the bill.
The issue is playability; to detach the gun (without any special scripting, like another attached object that will rez and attach the gun), you need to drop out of mouselook, because you can't see the gun or your inventory window while in it. This can make the camera view go behind a wall if you are standing up against one, is disorienting if you need to be moving, and so on.
Anyway, all that is very hard to do while under fire, even something as simple as clicking a door or hatch to open it. With practice you get good at it, but it's really cumbersome.