(Google Translate calls it 'gainful employment', no idea if it's the right translation. What I mean is work for which you're getting paid money which you need to use to survive.)
As I understand it, the human work probably wasn't directly taxed. I'm guessing that what was taxed as the incomes of the humans. This may seem like a meaningless distinction, but the humans have other opportunities to earn taxable incomes.
All that said, you seem to be getting at the notion of a Universal Basic Income. It's an increasingly popular idea in some political circles.
I think the point Kalium was trying to make is that it's not possible to quantify the value of human labor without pinning it to the income someone earns from doing it. A programmer's job is less physically labor intensive then a farm worker's, who obviously earns less. And there are numerous skills and fields more complex then programming that nobody will pay as much, or at all, for someone to do.
For a machine, it's value is directly tied to the profits gained by it's operation relative to it's operating costs, which is the business income that is already taxed. I think the taxing of machine "work" jeena was asking for would basically just be an increase in taxes on corporate profits, perhaps with some variation based on how many people they employ relative to their profits.
There is, however, a more fundamental argument to be made against the notion that this kind of technology is neutral and that you can somehow stop management from making these kinds of decisions. It's not and you can't.
If technology exists to lower the operating cost of a type of business through automation, it's only a matter of time before one of the players in that business adopts that technology, to get ahead of their competition. As soon as that happens, all other players are pressured to follow or face the consequences. Often they cannot avoid adopting the technology as well.
The flip side of this is that if you can be the first to create and market this kind of technology, there is a good chance it will be very lucrative, so there is a lot of pressure to do so. It's almost like the technology wants to be born.
As a result, if it is possible for a robot to be created to take your job and do it cheaper, it is very likely that someone will do just that at some point. We could of course all agree to not create such technology or use or buy it (if we think this is better for everyone), but this makes it even more lucrative for some other company to come along and break that agreement (prisoner's dilemma).
So far, robots are mostly taking menial jobs that most people do not enjoy a lot. I am not convinced we should prevent that. What I do believe is that we should offset the loss of income so people who lose menial jobs can be compensated and pursue another occupation that is – hopefully – more meaningful than what the robots took.