Uncle Bright Star seems so dark, so cryptically evil almost, yet he has a heart of gold. When we first meet Uncle Bright Star, we don't get why he comes across as so intimidating. Why does he stand in the way of reuniting Moon Shadow and Windrider with Mother, for example? Why is he so against Windrider when it comes to his dream of flying? But we soon learn not to underestimate how awesome Uncle Bright Star is. This is a man who has been around the block more than a couple of times. He's been in America longer than anyone else that we know of in the book. Heck, he was there to build the Transcontinental Railroad. So, if he seems jaded and really suspicious and stone-hearted, it's probably because he's had to deal with a lot of prejudice and violence in his time as a non-English-speaking immigrant laborer in America.
When we take this biographical information into consideration, we start to understand why it is that Uncle seems so hard-hearted. He's a pull-yourself-up-by-the-bootstraps kind of guy who's worked hard to earn what he has. He knows what it's like to not have people to count on, so he cherishes the Company and the dream of brotherhood that it offers. Windrider's dream of flying can be seen as a threat to this dream of camaraderie and shared goals.
But before you think that Uncle Bright Star is too stubborn and stuck in his ways to imagine another person's way of thinking, remember that he does come around to supporting Windrider, and he does show that he cares very deeply for people in his life. His love and care even extends to his untrustworthy and violent son, Black Dog. Uncle may threaten his son with all kinds of punishment (and have really nasty-sounding threats, too), but that doesn't mean he goes through with it. He loves Black Dog too much. And he's not so unmoving that he doesn't take to new people, like Miss Whitlaw, whom he lets sit in his throne. And most of all, let us not forget that Uncle Bright Star is a secret artist. On Moon Shadow's first night in America, Uncle hastily gives him a wooden sculpture he had carved into a Monkey. And he's so fidgety about being that vulnerable that he pretends like it's no big deal as a gift. But really, how sweet is that?
It's also worth remembering that we don't know much about Uncle Bright Star. We know he has multiple kids in the Middle Kingdom who live very well, thanks to his hard work. We know he brought Black Dog over, who has resented him ever since. We don't know anything about the mother of Uncle's children, whether she is alive or not. And we also don't know anything about whether or not he has made other efforts to bring family over. Presumably, from the way he dissuades Windrider, he does not support Tang women being in America, and maybe Black Dog killed his hopes for having his sons thrive in America. Again, this is all conjecture; we'll leave more thinking up to you.