How important is free speech and for whom should it be protected?

Free speech is the thin veil separating us from the tyranny of ideology. When one group manages to eradicate another group's freedom of saying what they want, that leads to a kind of brainwashing. If everyone is only allowed to hear what a certain group says we're allowed to hear, isn't that brainwashing? When we lose our freedom to say what we want, it will only be because a certain type of speech is imposed, and others are denied.