they're called leecher mods because you can use them for leeching
Using a leecher mod doesn't mean you are a leecher though. If you upload and share as much as you would when using official mule, but benefit from the improved upload algorithms, then I don't count you as a leecher.
Official emule is meant to be a slow downloader because the slower it, the longer you upload, the worse your U:D ratio gets and if it's worse for you it's better for the network. Any mod that improves your U:D ratio will be worse for the network then official.
You're not directly harming the network by using a leecher mod, but you are giving less in return then you would if you would use official.
Yes, ketamine is one of the other leecher mods. I've never used it but a lot of people like it. It's gotten a lot of attention due to an 'undocumented' spamming feature an older version has...
Ketamine isn't even a true leecher mod. It's not possible to disable upload and it's not even noratio. The noratio ketamine is only for 'very special' people