Practical Reasons for Free Speech
While many people support free speech, most of the reasons given are ideological rather than rational. Here are some practical reasons for the necessity of free speech.
First, you never know who would have something useful to say. With free speech, people can articulate problems and propose solutions that the person in a position of power may know nothing about. Someone who is a complete nobody can come up with valuable thoughts; and the only way to reap the benefit of that is for there to be free speech.
Secondly, free speech makes it possible for people to say their perspective - a perspective that once again may not be known to people in positions of power. With free speech people can express the reality of their lives and of the world as it impacts upon them. Then it becomes possible to understand this reality and to make more informed decisions.
Finally, free speech makes it possible for people to articulate their feelings and their thinking. That in turn makes possible negotiation and achievement of reasonable solutions. You can't deal in an informed manner with someone whose thoughts and feelings you do not know. Whereas if you do know their thoughts and their feelings, it is possible to use intelligence to work with them and negotiate workable solutions.
The best reasons for free speech are not ideological ones; they are practical ones. And the more people understand this the more they can do to defend free speech.