I will never understand the people, and that is a very general remark, meant exactly that generally, who complain about others critisizing things. Yes, people who always complain about everything and don't value any beauty or positive surprises when they come up, who only try to find fault with everything, are annoying and depressing. But things don't change for the better when everybody just goes "oh this is fine, could be worse, look at the bright side, I enjoy everything no matter what".
For improvement you usually need critisicm. And people also critisize because they care and want improvement.