Some people just like to kvetch. Some people will heartlessly scare you with horror stories because it somehow makes them feel better. Maybe they feel like, if they can talk about this, then it demonstrates how strong they are. If such people have given birth then they might needlessly upset first-time mothers with chatter about their own bad experiences. Those people are the ones that the article in your opening post refers to.
If a mother has had bad experiences while giving birth, but she can use it to offer advice to other expectant women, then it’s good for her to share her thoughts.