[Unosolo]

Existing tax systems burden labour more heavily, than capital. This is because capital can flee easily, but labour cannot. A dollar doesn't have a spouse, kids, parents, siblings, a social circle, it doesn't need to learn a new language or culture - it can be moved with a speed of light at a very short notice indeed. Since deploying dollars is cheaper than deploying people from the tax prospective there is a strong economic incentive to replace people with capital at workplaces.

Since Bob's productivity will increase threefold and the demand is finite it is likely Rob, Bob's mate, is going to loose his job. Now the two of them are going to compete for a single job opening and Bob will be lucky (and thankful) to stay employed with no real leverage in his salary negotiations (Rob is unemployed, lost his house and now very eager to get that job too!)

The extra profit will go mostly to the robot owner with some to the robot's inventor (although once enough people are capable of building robots the inventor will have diminishing leverage too, unless he keeps coming up with better stuff).

Then the argument goes that Rob would then become a robot inventor or a capitalist instead of working the mundane job at the widget factory. Not going to happen. He is 53, he doesn't have the capacity required and he is not going to develop on at this stage. No one is going to bet her money on Rob becoming a millionare through invention or investment or even making a decent living ever again. Rob is sad. Whenever Bob talks to Rob he is scared to loose his job to more automation.