GitHub's Trending page has previously featured many similar projects, open letters and other non-software repositories, so I don't see how this is relevant here.
I understand that not all readers are interested in or even affected by GitHub's acquisition; however, a large number of them are. For this reason, a downvote button would be significantly more effective and democratic than giving two or three users the ability to completely hide a popular submission they do not agree with.
I do believe that dang and the Hacker News moderators have developed a good sense of how to keep the community healthy. Unfortunately, the most reliable way of accomplishing this is to eliminate any and all controversy that could lead to debates and arguments. This, however, is not indicative of a good community, it simply places users in a filter bubble by only showing them content that no two other users have ever disagreed with.
Despite eliminating nearly all arguments and controversy, this nonlinear voting mechanism is dangerous to the community and society as a whole, even if it gives the impression of a healthy community. Removing controversial submissions just as quickly as spam, child pornography and incitement to violence as can be expected from oppressive regimes is not an indicator of a healthy community, but rather that of a community that only gets to see what everyone agrees with.
Many people who have spent much more time on Hacker News than I have agree that there is room for improvement (see, for example, the analysis from last year that I linked to above). Unfortunately, simply hiding all controversial submissions saves the moderators time, and it seems that they are currently not interested in investing additional time into creating a truly healthy community, one that is capable of remaining healthy despite openly holding and expressing different opinions, and thus the current form of moderation is likely going to remain as it is now.