The limitation with ghost leeching is that it won't help raise your ratio. It's a way to avoid decreasing it (by never reporting download). If your ratio is bad and for reasons you want to increase it, you will have to generate upload one way or another. You can ghost leech and then seed the torrent you downloaded, but it can also look weird that you are now seeding a torrent that you never downloaded. But due to the nature of torrent, it is also possible.

But that's what I find fascinating. BitTorrent is a very cool tech, and not that hard to understand. It uses a lot of simple idea that works very well together. It's really fun to hack on it. And I add an obsession with findings 'cheating' methods a few years back. Overall, as you said, it's more of a social contract. None cared unless it was stupidly obvious.