Published text is probably one of the worst mediums for people who wish to contradict themselves without acknowledging it. In speech, you can lie about what you’d previously said, and most people won’t retain a clear memory of what was actually stated. But in text, we can simply look it up.
With Internet comments, it’s even easier than most forms of permanent communication: we need only scroll the screen up a bit, or at most click on a hyperlink, and we can instantly review the text.
So why do people still try to get away with it? Is it because that strategy works so well in normal life that most people have never even felt the need to examine it? Human psychology is a mystery in so many ways.