Possibly because - in addition to all the other reasons mentioned - it's simply **** ill-mannered.
I'm not sure how manners come into it really, that's an odd statement.
Two reasons- I used to work in Woolies and we found used wrappers etc stuffed inbetween the shop fittings and in displays DAILY.
Car drivers often speed, do we ban all people from driving because they might speed? What a daft reasoning. As is the card issue, there are always ways around it in the unlikely event that your card is declined.
Like I say, the only reason I can see for disliking the idea is that some grotty members of the public think it's OK to steal by that route. But it doesn't mean that all do, so thinking that is totally irrational.