If you do it this way, you're an ass. If nobody is behind me I'll back in but I'm not going to inconvenience people like you described. I used to back in at my old job in a crowded parking garage (but I got there at 6:45am before most anyone else) so I got pretty good at it. The parking garage was very cramped quarters so backing out was tricky (requiring a 3 point maneuver if you didn't angle yourself perfectly the first time).
if no one is behind you, I can't imagine anyone would criticize you.
in a crowded parking lot, though, I say that if someone was that concerned with not being able to safely reverse out of a parking space, just park further into the lot where you can either pull forward or back into a spot without holding up other drivers.
in my parking lot at work, I'll usually pull forward into a space but then have to back into it to get my parking spot back after leaving for lunch. it's a low-traffic lot, though... in the muni lot at home, on the other hand, I always pull into a space because it's a crowded parking lot and there's nearly always at least a couple cars around (if not looking for a space than using the lot as a shortcut)
