In many ways this seems to have replaced diaries as a way of organizing your thoughts prior to screaming them into the void, with the bonus of spam and random racist diatribes.
Perhaps bonus is the wrong word there.
It is primarily why I post on HN.
Same here. I often find myself writing similar things under similar topics, but the very act of writing a comment makes me refine my beliefs just a bit.
(And then I can always count on other people to call me on my bullshit, which is another learning opportunity.)