I wouldn't really call it "bravery," but I am not generally a fearful person. I'm an outspoken atheist in a Christian world. I'm a communist. I'm a revolutionary. I believe it's possible that the United States government, perhaps indirectly, will literally torture and kill me; and the only reason they wouldn't is that I'm too small potatoes to be worth the plane trip to wherever it is they torture people today.
As not fearful as I am, there are still things I think are true that I don't talk about, because I think saying those things would provoke a massive and hostile (but nonviolent) reaction. Basically, I think a lot of people would say mean things to me if I voiced some of my opinions. Again, I'm not worried about being doxxed or getting death threats; if I could be Anita Sarkeesian or Zoe Quinn, I'd do it in a heartbeat. But sometimes, I don't want a lot of people saying a lot of mean things about me, and so there are certain things I don't say because of that possible reaction.
I do not, however, feel that I'm being silenced or that my freedom of speech is at all being compromised. Unpopular opinions are unpopular. If you're going to express an unpopular opinion, a lot of people may say mean things about you. If you think they're worth saying, then you have to weather the reaction. Critics have just as much right to criticize, by whatever means available, as anyone has to speak in the first place.
In just the same sense, if you question the legitimacy of the United States government or the capitalist ruling, you have to weather the reaction, and governments and ruling classes hate having their legitimacy questioned, and they have lots of guns and people happy to torture whomever the government or ruling class gives them. That's the reality.
I don't shut up because of fear. It would be ridiculous if I feared torture and death less than people saying mean things about me. I shut up because the value of saying what I think is true is less than the harm it might cause.
For example, several of my Muslim women friends wear the hijab. I think it's true that the hijab is a symbol of oppression, and, of course, I think it's true that Islam is terrible because it is a religion. I don't talk about these opinions with them. I remain silent, but not because I am unsure of my position. I remain silent because, basically, at the level and in the context of our relationship, it's none of my damn business. The offense and unhappiness I would cause, the rupture of our friendship, far exceeds the value any remarks I might make. So I shut up. If they want to know my feelings on the hijab or Islam, they could ask me, or they could read my blog. They are not stupid women, and if they want to research the debate, they can do it.
I don't agree 100% with anyone. (The only people I don't actively disagree with at all are those talking about things I know little about (physics, biology, etc.); if I had any real expertise in those fields, I'm sure I could find things to disagree with.) But our world is not one where everyone dispassionately considers every idea by abstract analysis. Our world is full of fights, and I think fighting for justice is a Good Thing. The first rule of fights is that those on the front lines get to decide how to fight. If I don't think I have the legitimacy and will to be on the front lines, then I have nothing to volunteer about how to fight. If someone directly asks me for my opinion, I will offer it, but otherwise, whether I'm right or wrong, it's none of my damn business.
For example, straight, white, European-colonial, cis-gendered, middle-class men need no defense whatsoever against minor errors in the LBTQA-etc. feminist, anti-racist, anti-colonial, anti-capitalist fights. Are people fighting these fights always right? Of course not; no one is always right. But even if I think I'm right about some minor error, even if I actually were right, actually criticizing a minor error is almost impossible to separate from defending my privilege, and I absolutely do not want to defend any unjust privilege that I have.
If shipping straight, white, European-colonial, cis-gendered, middle-class men to concentration camps ever became a real thing, I would speak out, but of course, that's not a real thing, nor is it likely ever to become a real thing. Short of that, I shut up about criticism, and just offer my support and cooperation.
I shut up about things I think might be true not because I'm afraid of criticism, but because I don't want to be hard to distinguish from a real asshole without a very good reason.