I understand it but I think it is unhelpful and silly.
The more you say something the more acceptable it becomes.
Like saying "I'm gay" you mean? 
Or "My husband hits me"?
Or "I don't love my DH any more"?
Or "These are my symptoms, does it sound like PND"?
Are those self indulgent too? Or is your disapproval reserved exclusively for people who feel that parenting in reality is not how they anticipated it to be?
It's not unhelpful or silly at all to express your worries on line. It would be far worse, if someone feels they hate their DC, to bottle it up and not discuss it. Loads of threads on here offer helpful advice and insight to people who are isolated or possibly too ashamed to say something in RL for fear of being judged negatively by people like yourself who think they are being "silly" and "self-indulgent".
Sometimes being able to say something out loud or write it down on a public forum is really helpful. It means you have accepted the reality of your situation and then you can work out how you are going to respond to that. In other words, it's often the opposite of indulgence. Especially when it's a subject that formerly had guilt or shame attached to it. You are hardly likely to write a banner saying "I hate my kids" and walk down the high street are you. (That would be attention-seeking.) Posting on an anonymous forum? Not so much.
And there are massive pressures out there driven by consumerism presenting a very idealistic picture of motherhood which it is helpful to see contradicted.
Also, if someone is going through a difficult phase of parenthood, it could be massively helpful to hear that others struggle too.
(Btw I've just put the same words in the search engine and none of those threads pop up. You've screen-shotted them so they obviously exist, but people often put an "attention-seeking" title on a thread simply to attract posters. I's the content of the thread that matters.)