How can you make it easier for people to raise their voice? To stand up for what they believe?

Put them in a condition when they are not affected if they have something to say.
Otherwise you’ll always have enough power to control what they do or think.

If you’re the one in charge, you’ll likely think that you should always own the last words, but it’s not ok.

You can learn so much from the people around you. It’s only through humility you can accomplish more. And to do that you need to allow people to step up, to say what they believe.
People you trust, of course, but they shouldn’t be chained or worried about your reactions.
If they do, they’ll always avoid direct confrontation.

If you’re not allowing this kind of growth you should hope to have someone who’s vocal even if she has something to lose. Someone who’s near you that you can listen to.
Then, maybe, change can still happen.