I think you and I have much the same perspective. Here are a few related thoughts:
If people are re-uploading material that is already seeding (same resolution, same file type, etc.), I think there should be a good reason for doing so, and the uploader should be clear about this. For example, there are lots of torrents from the BelAmi studio with different actors in them. If somebody has a favourite actor, perhaps it makes sense to upload a collection of films having just that actor. In this case, I think the uploader should say, "this material is already here [and possibly give links to it], and I've kept the original file names so you can avoid duplicates."
If, though, someone is just grabbing a few existing files and reuploading them, especially with few (if any) pictures and a crappy (or no) description, solely for the purpose of scoring upload traffic, it's abusive. I don't think the site's software can be tweaked to prevent this, so it would seem to be a loophole. These garbage torrents are often quite obviously garbage…and they've become more prevalent in recent months. It baffles me to see that quite a few members will download them.
On another note, the reference to potentially underage material is troubling: If someone is going to share files, I think he has an absolute responsibility to ensure that there isn't underage material in them. Not wanting to "bother checking 1000 files" is highly irresponsible. Possession of underage material is a serious crime in most countries, and sharing such material puts other members, and the site itself, at grave risk. If a member does share underage material, perhaps he should get one warning, but a repeat offender should be permanently banned.
And for yet another note, I sense that some members don't realise that they can select which files they want to download from a collection. I use uTorrent, and it's a simple matter of ticking/unticking the box next to the file name before the client begins the download. That way, I can often avoid downloading material I already have, or carefully select material that I want and avoid stuff I don't. This presumes, though, that the uploader is using good file names. Sites such as Tumblr or XTube often have random letters and numbers to identify the files. It would nice if an uploader put in a more descriptive title, but that's probably expecting too much.