Self-proclaimed experts on writing often express contempt for the passive voice, whether they understand what it is or not. Language Log has a good discussion of what it is and where it’s a perfectly good choice. It covers obscure cases that most people don’t know about.
Rather than offering my own defense of the passive voice, I’ll just list some of my own favorite uses of it.
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights… (Declaration of Independence)
‘Tis a consummation Devoutly to be wish’d. (Hamlet)
This episode was badly written! (Galaxy Quest)
Seek for the Sword that was broken:
In Imladris it dwells;
There shall be counsels taken
Stronger than Morgul-spells.
There shall be shown a token
That Doom is near at hand,
For Isildur’s Bane shall waken,
And the Halfling forth shall stand. (Lord of the Rings)
I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character. (“I Have a Dream”)
Some people will tell you the passive voice should always be avoided, but they’re best ignored.