It's not so much about COMPLETELY eliminating humans. It's about the supply to demand ratio of human labor(skilled, and unskilled). As technology progresses, it requires less and less human intervention. This phenomena has already been shown heavily in many industries(like car manufacturing... which uses robot arms instead of humans for much of the work now).

Even when the production line, which helped to spark the American Industrial Revolution occurred, many years ago, this phenomena was felt, and wages dropped.

This isn't untested science fiction. It's the continuation of a trend that has been occurring for thousands of years... as technology, and efficiency increases... the demand(and thus value) of human labor decreases.

On top of this, the world population increases every day, meaning that there is an ever greater supply of skilled, and unskilled workers, that when coupled with the ever decreasing demand of workers, due to technology, has created a fleshed out pattern of decreasing human labor value.