I made rooms next to a Zombie spawner to make an easy Villager farm. I cured some Zombie Villagers and separated them away into a safe room with light, beds and locked it with a double Iron Door. I used one Wooden Button and one Lever for each 2 Iron Doors, so I could open a door until a cured Villager walks into the safe room. Now the funny part is, that some Villagers just opened the Iron Doors and walked into the dungeon room where the Zombie Spawner is and the result was disastrous. I lost my 60+ levels and most of the Villagers too.
So why can some Villagers open Iron Doors, or use Levers, or use Wooden Buttons?