I said myself that implementation wouldn't be practical, so this is more of a thought experiment. But in all these cases, I think the person who profits from the change should also bear the cost it has on others. So if you invent a way to increase productivity, there is no need to pay; but if your employer uses it to make their workers redundant, they should provide for their continued livelihood. Of course this doesn't really work when a different industry is obliterated (which is why this is impractical).

> And how long does this tax last? Forever? Are people still paying taxes for all the farmers we don't have to have anymore?

Assume for a moment that being a farmer were hereditary and they couldn't do anything else anyone would find of value. Then when you replace all of them by machines, you make huge profit, but also leave hundreds of people without income. In such a case, I think it only fair that the farmers and their descendants be provided for indefinitely.

That this tips the scale against automation is not exactly bad: if the farmers have to be provided for anyway, additionally maintaining machines to do work they could do just as well is a further cost that should be weighted against the benefits.

However, in reality most people can learn to do other work, so automation can still end up a net positive, even when the needs of the displaced workers are taken into account.

I guess the problem will solve itself when workers will either employ themselves as revolutionaries and looters, or the beneficiaries of automation pay the equivalent of this tax to prevent this from happening.