If we're just talking about restaurants in France, at least part of the higher employment costs are cancelled out-- relative to the US-- by not having to tip 20%, so the menu prices can be higher without actually passing all of that increase on to the customer.[1]

As for demand, it is always elastic. A lot of people eat fast food, and a lot of those people are going to be in a position where they're just barely fitting it into they're budget. Raise prices, and they're gone. That's not even getting to the actual elastic part where people actually have the money to decide either way if they're willing to pay at one price but not another-- that bottom group is simply gone.

Also you shouldn't focus just on the one example I chose. I happened to choose a discretionary spending activity because I knew fast food #'s off the top of my head, but the same thing applies to every single business with low margins and moderate labor costs. Even if you were right and every single one of them could raise prices without losing customers, that would also mean that the exact people we're trying to pay a living wage then have significant increases in their cost of living as everything around them raises prices.

[1] France may also not be the best example to compare to the US. Despite staggeringly astronomical wealth inequality in the US, it still has a lower poverty rate than France. Canada would probably be a better example. https://en.wikipedia.org/wiki/List_of_countries_by_percentag...