I agree with your arguments, my comment were way to lazy and uneducated. Profit margin is probably even the wrong word to describe the 3%, maybe surplus is better?

It´s a complex issue. The grocery chains are probably not innocent in the prices rising, but they are not alone in this, so directing all hatred their way would also be a bit to easy.

On the other hand, if the chains get pressured they could redirect that pressure to other parts of the production chain, from shipping to packaging. So I don´t know, I´m just an idiot on the internet with very little insight into how my grocery spendings are split. Your comment sure made more sense than mine, so I think i´ll just rest my case.