Re: Bah!
My doors are much more substantial than cardboard. They're reinforced to the point where going through a window or the wall is an easier option. The interior doors aren't all that tough, but kicking through the drywall from one room to the next is too easy to put in solid core doors.
I looked round a flat in London which the estate agent had said was in a very good area i.e. low crime. The external doors all had solid metal cores, the windows all had inch thick bars across them and the locks were reinforced. There was an alarm which was top of the range and despite the bars on the window there were also window locks. It made me laugh when the agent told me that she thought the current owner was a little bit paranoid.