I think preventing the building of anything other than croplands when consumption of crops almost equals production of crops might well be the difference between the ability to actually build civilisations and the Travian, Astro Empires, Ogame, Zorg Empire etc etc built in by design supremacy of despotism.
In the games designed specifically to ensure the supremacy of despotism the dominating strategy is the roving horde of barbarians. For example in space games of that kind you basically live in fleets, always on the move, carrying all your resources with you, because like sharks to stop is to die.
If the skilled citizens and technicians and professionals responsible for producing the artifacts of civilisation refuse to build facility for anything but crop production whilst such swarms of barbarians have picked their village to base themselves in, or when "their" military consumes so much crops that the village would come to depend on them instead of on crop farmers for food, that might help put in place Freeciv's assumption that despotism is not necessarily the best form of government and being a barbarian horde not necessarily the dominant strategy.
Thus so far I am not convinced that removing the crop usage check that occurs in the building option would be a good idea. I expect it would simply cause the game to devolve into yet another game in which civilisation can never win against barbarian hordes.
(Did civilisation ever win against barbarian hordes, or are we simply the barbarian hordes who won out against the other barbarian hordes?)