This seems like bad advice to me. Is it based on the idea that any negativity is a bad thing? Or is it simply that you don’t want to make a fuss?

Because expressing dislike at something, otherwise known as having an opinion, is vital as a person and it’s vital that everyone recognises when they do or do not like things. Shutting your mouth and repressing those feelings is A Bad Thing.

If you are obsessing over negativity, that could be construed as unhelpful behaviour, however complaining, per se, is not.