What if the person in question can not make it to the beginner classes and can only attend at the time of the advanced class? Should they not be allowed to study Aikido? Most towns don't have multiple Dojos.
In all of the other Matrial Arts I've studied you have to spend time teaching, thats part of the training.
I can't imagine every class you get stuck with the beginner, so every now and then you have to give a little back of what you have recieved. Not so bad!
I ask one of the shodan at my Dojo if I could attend the mixed class (the more advanced class). Being a wise man he said "you pay your money, you can attend any class".
If you don't like working with beginners why don't you ask your Sensi not to pair you with any. You know, explain your situation
and see what he has to say.
Thats my 3 cents, proably one cent more then I should have said!