I'm not suggesting for a moment that you did talk about berating customers - that was my own wider consideration of how it could come across if you don't have the bags freely available for the people who will expect them. I was not twisting your words but adding my own on this discussion forum.
For what it's worth, I take my own bags in; but I've observed that virtually nobody else ever does. I don't have any 'agenda' other than to realise that working in a shop for low pay at often unsociable hours is not most people's dream job - and that it's probably even less fun to have to put up with the negative reactions of, and delays caused by, customers who are expecting you to offer/pack a bag as a basic part of serving them and which they obviously need, but then you don't.
Not all, granted, as many will indeed politely ask for one or more bags; but a fair proportion won't. Even just one customer abusing you for being "too stupid to even know that I obviously need a bag" is one more than you want whilst doing a not-particularly-exciting job.
It really isn't especially important to me, contrary to what you may think; just my thoughts in response to your own thoughts.