When I say something doesn't belong on Hacker News, I don't mean it's unimportant or doesn't matter. I just mean that it isn't what this site is for. There are many, many stories that are relevant and important to me personally that are still not appropriate for every site I go to.
Think about it this way: Would you go on a My Little Pony fan site and post this stuff there? Human rights are just as crucial for My Little Pony fans, but it's easier to recognize that they aren't appropriate for a single-topic site. Hacker News is not a single-topic site, but it is still a site with a focus. If you look at the guidelines, politics are explicitly called out as being off-topic.