What about the Depression, the dust bowl or all the floods? Our ancestors would have been only too grateful to have had access to a store when crops weren't available. Almost every missed or late delivery I would not have been able to walk out into my garden (if I had one) and harvest anything either. This is not like the US Mail, weather, machinery failures and injuries happen and you can't count on unpredictable circumstances that happen to us all.
Don't sign up if you're not committed because you hurt the rest of us. I personally don't mind going to the store a few times a year for produce, it makes me appreciate the CSA more when I see the prices and the quality. It also makes me grateful that most of the time, I get my stuff delivered right to my front porch.
Sincerely, Local Farmer Supporter