It seems that since The Slug Club is really a personal club and not a "Hogwarts" specific club the criteria can be whatever the professor wants it to be. I feel that if it were a "Hogwarts" club or activity sponsored by the school like in a muggle school (ie. yearbook club, glee club, or german club) it should be more inclusive and promote more student cohesion.
no subject
Andromeda//Hufflepuff