We downweight bilious comments, especially at the top of threads. Why? Because the internet tendency is to make everything ill-tempered, peevish, and gross. The spirit of this site is curiosity (https://news.ycombinator.com/newsguidelines.html) and for that to have breathing space, there needs to be an active counterweight.

The main thing to understand is that it's a global optimization, not something stupid like supporting particular PR campaigns.