But the best kind of ad is the kind the enduser doesn't realize is an ad. Not to mention that cross-posting happens all the time so your "ad" can make it all over the site for a day or so. And if it goes viral enough on reddit, it'll inevitably be picked up by a multitude of websites built around leaching content from reddit. Obviously there's no guarantee that it'll work any given time, but try it enough over a span of time and I can see how it would be more effective than traditional advertisements.

It's why Facebook ads look identical to posts at a glance. If you don't know it's an ad, you're more likely to click it, share it, like it, etc.