Susan

The true problem is destruction of all villagers when spawning near a village or exploring within range of an as yet unknown village. There is no opportunity to flip the doors or protect the villagers (as you have not yet discovered the village. eg. it may be over a hill). The entire village can be wiped out in one night.

Village doors continue to be generated backward allowing zombies to infect the villagers. This has occurred in multiple villages in the latest beta (1.8 ) as well as 1.7.4.

Example: seed- Caprice (tried in both 1.7.4 & 1.8 beta (14w06a & 14w07a, at least)

village coordinates 141/69/280
12 buildings
5 buildings have no doors
3 buildings have correctly placed doors
4 buildings have backward doors

I watched in creative as zombies came to the doors. All villagers in the houses with backward doors were infected. None were infected in houses with correctly placed doors, even by baby zombies.