Earlier quoted context omitted.
> Now I wonder how clients protect themselves against abusers (i.e. people who never upload a single bit but only download). It's called leeching, and it depends. It's typically considered good etiquette to upload as much as you download and that's usually enough, but it can be enforced https://en.wikipedia.org/wiki/Leecher_(computing)
I have the opposite problem, many things I download seem so well-seeded (seedboxes?) that I rarely achieve any sort of respectable ratio even if my uplink idles most of the time. It might be client problem but I haven't found much anyone discussing this. TAKE MY BITS!
If the torrent is already well-seeded it's ok, a 1567th seed won't make a difference so don't bother with them. It's the less seeded torrents where you can put some efforts and do something good.