I think it would be fine if amule doesn't share every category dir.
So, amule moves downloaded file to a specific dir (just like now)
automatically, and YOU can choose what you want to share or not.
Right now i use categories to move file when downloaded but i have to move
manually every file that i don't want to share as well, so why use categories?

There is a list where you can choose which dir to share, let's use it.

So, keep only the incoming dir as shared by default.