The way you phrase it (but maybe I get you wrong) suggests that the customers are somehow in their (moral if not lawful) right to do this because of previous policies from the supermarkets. They (supermarkets) may have been wrong, but so is stealing. They don't cancel each other out, nor do two wrongs become a right.

I'd say stealing is always a net negative effect for the whole.

But if you're saying that the entire context explains a lot of the behaviour, and could possibly be predicted, then yes I agree.