There's a finite population that a single planet can hold, so there will have to be some form of population control eventually.

Now, why the heck would you (the farmer entrepreneur) care about what the government does with the taxes it generates from your revenues? The question is: is your investment profitable enough? Everything else about your scenario is politics and, in a democracy, these things are decided (or supposed to if you drink from the cynic's cup) by the population.

If the farmer (as a person) disagrees, he can just not buy or buy in another country or planet or whatever. A post-scarcity society has value enough for some of us that we'd run such an automated farm for little profit if only to selfishly sustain said society.