I wonder what the original leak looks like... Whether it would be as mineable as the Ashley Maddison leak, or whether you'd have to burrow down into each and investigate manually.
You're right, but that increased cost is minimal, and one many people seem willing to pay. I've seen green troll accounts pop up like weeds in many controversial threads. They're easy to spot because most of the time the usernames are thematically linked to the persona or the thread they're created for. Casual use doesn't seem to be deterred.
The increased cost is not only minimal. It's actually nonexistend compared to a site like 4chan. You have to fill in a captcha for every post. Here you only have to fill a captcha on account creation.
Trolls exist, but hacker news is no 4chan. I think it's enough of a deterrent to keep atmosphere generally constructive, while not eliminating all low-quality posts.
You're merely deluding yourself into thinking that some stupid voting system can eliminate low-quality posts. Using it to give higher voted posts more visibility is okay but thinking that these magic points are representative of quality is a stretch.