For site survival purposes, it's not enough for a comment to contain interesting content, just like it's not enough for food to contain nutrients. It also must not contain poison.

It's helpful when users gently ask other users to stick to the guidelines (https://news.ycombinator.com/newsguidelines.html). Of course it's also off topic, but that is a necessary evil. Out-of-band control signals are what enables the system to right itself. munk-a's response was perfect.