1). I hardly think you can call it "working for the supermarket for nothing" if you pack your OWN shopping. It's not exactly cleaning up the broken eggs in aisle 12, is it?
2). Nope, the cashiers will be deployed to other departments like merchandising and stock control. You know, so that all the stuff you put in your basket isn't out of date or hasn't got the wrong price on it.
If you don't like them, don't use them, but don't moan about waiting for a checkout in a queue six deep when the self-service is free...