They probably assumed that droids wouldn't have the initiative or foresight to lock a door on them in the first place, or be able to get through one in their way. I get the impression independent thought among droids was heavily discouraged, hence memory erasures and so forth.
In addition to the stormtroopers being somewhat reminiscent of Nazis, I've heard that the Emperor was at the time of the first film conceived as being like Nixon, flouting the law with impunity and drawing greater power unto himself. Which as was said would have resonated more with 70's audiences, what with Watergate and Vietnam still weighing heavily on the public consciousness. Nowadays the shock of that sort of thing has worn off, with mindless patriotism making a big comeback. I always thought the rebels would have had a fairly tough time of it trying to establish a new government, since the 'silent majority' probably supported the Empire and didn't pay too much attention to whispers of the horrors being perpetrated. Things like Alderaan would certainly have been kept secret or written off as rebel terrorism by the official news sources.
(Of course the announced intention of the Death Star was for rule by terror to prevent the growth of the Rebel Alliance, but with its subsequent destruction a few days after its first use, the official announcement of such a policy would have had to be drastically altered.)
