We did get along better as we grew up more, so it's not like we hated each other forever. And some people, like the Fire and Sky Tribes, like the legend too much to tarnish it with honesty. [It's a good question. What happened in those two villages that didn't in Hakuryuu's, anyway?] Well, it's just speculation from my part. Maybe that Hakuryuu didn't teach them that at all, and it just so happens that this Hakuryuu had a similar mindset.
King Hiryuu had presence and charisma, but he wasn't particularly powerful. I'm not sure if he would've forced us to come because we were there on our own will. Just one day these dragons came for us, offered us powers in exchange of protecting the king, we accepted and went. He wasn't involved. We weren't forced to drink the blood. I don't think he would've forced you to do anything though, he was so nice.