Well no one else is around to open the door if I'm here alone.
If I peep and see a jehovah's witness/chugger/guy with teacloths then I might hide, but only if I think I haven't been spotted.
Otherwise, I open the door.
In fact - thinking about security - we were burgled last year. The burglar was seen knocking on our front door (by my neighbour, I was on school run, she ran inside and hid because she thought he was selling something 
). Obviously no one answered the door. So he took the opportunity to go round the side, break in through the back door, ransack the house and nick anything portable (while looking for my husband's car keys).
If I'd been in, I'd have answered the door and am certain he would have pissed off. So now, I actually worry more about not answering the door, particularly if am feeding ds2, because then ponder the chances of someone scooting round the back.