The only helpful advise given to my wife was that she needs to put actual physical distance between herself and her mom. To move far enough away so she could limit in person interactions to a couple times a year.
If a grown up child thinks parent should've fixed their flaw before it affected the child, then they presume that the flaw could have been fixed or mitigated.
In that case, why the child spends time blaming the parent on reddit now, instead of working on fixing the flaw that was, in many cases unknowingly, created by the parent?
No. That's not how it works. Understanding a cause of a behavior is not the same as denying responsibility for the behavior. This sort of thinking is what leads to the (extremely flawed) conclusion of "I was abused, and I turned out okay, so your behavior because of your abuse was your decision" thinking.
What you're doing here is victim blaming. If someone abuses you, this is not your fault. If, because of this abuse, you have social problems you're still going to have to figure out a way to deal with these problems. Understanding the root cause of the behavior (ie; my mother molested me, thus I have a strange view of sexual norms, thus I engaged in abusive sexual behaviors) can help in the treatment of this behavior. In fact, I would go so far as to say that understanding the root cause is almost always needed in order to treat the behavior.
You make the extremely flawed assumption that by exploring an understanding of causation (abusive parent in this case) that the person in question is not working on fixing the flaws. These ideas aren't mutually exclusive. And for many people, groups, including reddit groups, act as a way to work through their problems with others capable of relating to their situation.
If someone's entire course of action is "my parent was abusive, so I'm going to keep engaging in this behavior because now I have an excuse" the problem present is this person's continued desire to behave poorly. It doesn't absolve the parent from their portion of creating the problem, nor does it absolve the person in question from engaging in the behavior.
Tl;dr- No, none of your points stand on their own.