Never-ending debate here and I don't think you'll get a satisfactory answer, for what it's worth. My humble opinion. The aircraft seats are designed with a recline feature, and the occupant of the seat can choose to take advantage of that feature at his/her discretion. However, unless the seat is a hard shell seat, where the recline does not impinge on another passenger's space, or if the flight is a night flight or an early morning flight when it is reasonable to expect people to be sleeping, I think it is rude to recline to max, but that is just me.