One could make an argument by comparing the effect on productivity by either replacing the worker or the machine. When workers are readily available (and machin

One could make an argument by comparing the effect on productivity by either replacing the worker or the machine. When workers are readily available (and machines are designed to make workers replaceable), it doesn't matter what a time-transplanted peasant would do. The required skill level when using older tools and processes (welding and other building processes) is typically higher than with modern tools. This makes workers more replaceable today. Modern tools make productivity less dependent on the skills of workers. It's not a moral argument, just a fact that explains the observed phenomenon.