Earlier quoted context omitted.
"Taxation is theft" is true regardless of whether robots are employed or not. The fundamental issue is, simply, that it involves the use of force (or threat of use of force). As long as men with guns will come and arrest you if you don't "pay your taxes" then it is theft. No rhetorical flourishes or byzantine logic can alter that.
If your definition of "theft" is "taking something by (threat of) force", then (1) private property at least of land clearly is theft, (2) one could even go further and argue that some forms of taxation aren't theft, and (3) police are regularly involved in theft even while doing the right thing. The key is in "taking something": there is a baseline state of the world against we're comparing the current status quo. F…
That is not my definition of theft. Theft by force (or threat of force) is a subset of theft in the more general sense.
For point (1), there is clearly a historical baseline in which no land was owned by anybody, and all land was equally accessible to all. Then people started to make claims that some part of land was theirs, and that they had the right to exclude others from it - if necessary by force. They took something from others by (threat of) force - hence committing theft according to your definition, and this theft is enshrined by modern property law.
If no land was owned by anyone, then taking a chunk of land is not taking it from "others". Its taking something which was previously unowned.
The origin and nature of property rights IS an interesting discussion, but it's really a red herring here. Consider this: You live in the proto-world with no land ownership. You select a piece of land that is unoccupied and unowned, and you build a home on it and start a garden. Later, somebody else comes along and says "I want your home and your garden for myself". Would you argue that you have no right to say "bugger off" to that person? Are you saying you have no right to defend that home and garden, that you worked on, toiled, and cultivated?
If not, how do you propose mitigating this conflict?