For example, while people may refer to a project as "their baby", the "calling someone's baby ugly" analogy stretches the metaphor to the breaking point. A baby's appearance is set and there was nothing the parents could do to affect it in the first place. Constructive criticism of a project, on the other hand, can serve to improve the project, as well as being instructive for anyone working on similar projects in the future.
Of course, the author then does say that "disagreeing" is OK as long as you do it tactfully. OK, fine. But that there's a word for that: "criticism".
Finally, we have this notion:
>Along this same idea, it is good to not talk about problems without offering up solutions. Doing this is called complaining.
Proposing solutions before discussing the problem is a cognitive antipattern (see http://lesswrong.com/lw/ka/hold_off_on_proposing_solutions/). If you try to solve a problem without carefully thinking about it and discussing it first, you will arrive at inferior solutions.
We should try to respect other people's feelings, but we cannot do so at the expense of progress.