And eventually all this will be primarily automated, with a few humans contributing because they love to develop things in science, engineering, etc.

Can you imagine someone willing to do those things because of some reason other than monetary gain, as it would be in OP's world? How many people currently stuck in Jobs would work toward accomplishing these things with the idea of ending world hunger, because they _want_ to do it, instead of having to do it because they have student loans and bills to pay?

I don't think there's anyone out there working on solving world hunger because they have loans and bills to pay. It isn't a monetarily profitable endeavor.

People have to have the buying power to support the chain you describe. If the buying power of a population vanishes, such as by being made superfluous, they get a large population reduction whether they like it or not.