You are talking about boycotting Carrefour as they treat the farmers with disrespect, look what happened in the 1970s in the UK, Tesco changed the way the Brits shopped, this effected every farmer who up to that point were operating cartels with local suppliers and getting grants from the government to produce food stuffs to be stockpiled, this lead to food mountains. suddenly Sainsbury's said they were only going to take milk from suppliers at a certain price, once this happened the other supermarkets started to control the pricing of all goods. the poor farmers had to give up and move out of farming.
Now tesco and the rest buy products from their own farms and invest money in the development of better care for animals and produce. Yes the farms have had their profit reduced but they do make a profit.
who ate UK apples in the 1970's, did you know they were weekly sprayed with lead arsenic compounds to kill pests, now no UK apples are sprayed with any dangerous and harmful pesticides, it is all down to the general public who voted with their feet and with the aid of the big supermarkets.
Getting back to the original topic, the supermarkets in France, as with all France, are lagging behind what you would expect from UK or US supermarkets, by about thirty years. They will soon catch up eventually.
By the way I know several farmers, and even though they plead poverty they are quite well off, one is the largest land owner in Northumbria. Never belief what a farmer is telling you.