If we have the technology to replace those people and we don't do it, then we as a society are already supporting them just to survive. You're talking about artificially maintaining inefficiency. If we're going to go down that road, we might as well start paying people to dig holes and fill them back up again.

The 40 hour workweek is significantly shorter than the 6 12 hour work days people used to endure.

Why not reduce the workweek again, to say, 32 hours?

It's not a 'natural' evolution, but organized fight from labour.

The same with the general conditions of work: https://en.wikipedia.org/wiki/Mines_and_Collieries_Act_1842

So, in my opinion, reducing the workweek or, an alternative that I think is more practical, stop working younger it's against powerful interests and can't be done without a fight.

The transition will be difficult (they usually are) but the end result (more free time for everyone) sounds good to me.

Honestly, I think this is never going to actually be the case. Why would a grocery store lower prices just because their costs went down a bit? Neither the demand nor the supply has changed, nor has the price people are willing to pay for their groceries.

If nothing has changed but your costs, why lower the prices when you can simply report increased revenue to your shareholders? If competition comes along, a quick "we're premium, they are cheap" marketing campaign (or buying them out) would probably cost less than lowering the prices to match.

I think it's fair to say that even if Walmart could half their operating costs with technology, those savings would not find their way into the pockets of consumers.

It can, that's clear, the problem is convincing the people who didn't lose their jobs that they should take a take hike to support the others; that's not an easy sell in Western Capitalism at least.