When I started at my current job three years ago, office doors were never closed. All telephone and face-to-face discussions were had in the open, for all to hear. In the last few months, almost all conversations have been whispered behind closed doors.
Three observations: (i) once one person starts shutting their doors, others will follow, (ii) once you start closing your door, you will continue to do so indefinitely, and (iii) once you start closing your door, you will effect a definite, noticeable change in the office atmosphere, for better or worse.
Just sayin’.