Artistic License - Economics: No, not the Lunar anarcho-capitalism championed by the author's various mouthpieces. Reasonable minds can (demonstrably) disagree about the workability of that. But the premise of the central conflict in the book, that control over Luna is economically important to Earth because it produces foodstuffs, makes completely no sense at all. Since the technology exists to drill tunnels in rock and grow large amounts of food in said tunnels under artificial lightning exists, why not drill some farming cubic in the Himalayas, much closer to home and easier to police? We're told that Luna has lots of solar power, but also that practical fusion power exists in this universe. Why go to the moon at all?
lack of space? The earth's population is 11 billion in the book, and the moon's biggest customer was India.
The Earth's land area is still bigger than the Moon's.
Yes, but as Prof points out in the book, Loonies don't live on the Moon, but in it. They measure in cubic, not area.
One 11-billionth of the crustal bedrock under India alone is several times the (above-ground) volume of the Pentagon. You need to leave some rock in place for structural support, but how much cubic do you need to to feed a man?
More importantly, how do you power it? The Loonies use vast amounts of solar power, with some fusion as back up. It's implied fusion isn't cost efficient enough to use alone to supply the moon, instead almost everyone has vast acres of solar panels that in other heinlein stories are implied to be 90+% efficient.
Fusion may be too inefficient to supply the moon, because hydrogen is a scarce resource there. But Earth has oceans, which are 6 % hydrogen by weight. Once you get fusion up and running at all, its efficiency becomes a non-issue, because your fuel supply is essentially unlimited. (The cost of liberating the hydrogen from water molecules is negligible compared to the payoff from fusing it).
Considering the leaders of the world they probably refused to tunnel under the the Earth, each country fighting because their land is "special", they couldn't possibly deface it in such a way. Much easier to force others to do the dirty work on a rock no one cares about.
It may be impossible. There is no guarantee the mining techniques used on the moon could be replicated on Earth with 6x gravity.
It probably has a lot more to do with the political system on Earth- it's a "Planned Democracy." If they grew the food on Earth, it would be confiscated under the Federated Nations Charter, or perhaps sold on the black market. By growing food on Luna, it comes in through an FA agency, and can passed on to politically connected constituencies in the FN, particularly in India. Remember, parts of FN undergo planned famines as part of their political process- presumably these punish groups that won't pay ball with the managers. Take a good look at the parts where Manny and Prof are on Earth, and see what you think.
It is never really stated how much food Luna produces. According to one newspaper, it feeds "a hundred million Hindus" but, as Mannie points out, this grain only "makes the difference between malnutrition and starvation" so really, this grain is probably less than that provided by the Midwestern United States, but imagine if they tried to secede, and slapped an embargo on America? People would starve.
Because you'd have to keep reboring the holes (gravity on the ground above tends to shrink them), and you'd have to figure out a way to keep the lights powered continuously (no clouds on the moon, and very long days)
Long days mean long nights. If the rock's got rotation, it'll come out even half-day, half-night, regardless of rate. What you don't have on the moon is surface development (cities, roads, the like), so literal solar farms would have a place to be. Though, solar might be hard on upkeep. No atmosphere to burn up small asteroids. Equipment could get wrecked.
I think the main point being missed here is that it's stated IN THE BOOK that the lunar colonies DON'T produce any significant chunk of Earth's food supply. The reason they have to rebel by force is because the earth governments don't want convicts running around free.
And because they'll die very soon if they don't. Mike estimates at the beginning that Luna has only seven years until the starvation and food riots begin, and cannibalism comes in two years after that.
They make enough to be valuable, give the Lunar Authority importance beyond being a dumping ground. But they don't feed the planet or even india. But they do produce more efficiently because Heinlein envisions very high efficiency solar cells and batteries able to produce near perfect growing condition.
My take on this was that FN and the Lunar Authority claim that Luna produces a large portion of the Earth's food as a way to keep a stranglehold on the Loonies. As the book points out several times, earthworms aren't going to take kindly to Loonies setting up their own government if it means they lose their gravy train.
As an example, the opposite occurs in the Isaac Asimov novella "The Martian Way". A demagogue on Earth was claiming that water shipments to Mars was detrimental to Earth, despite the fact that at the current rate of consumption, it would take millions of years for Mars shipments to make even a dent in the Earth's water supply. Something similar could have been going on in this book.
Mike keeps updating the odds against the rebellion to be worse and worse, even though the rebellion is going perfectly according to the plan they intended before it started. This doesn't make any sense. If things need to happen at the beginning of a plan for it to all work out, and they do happen as planned, then the odds that the plan will succeed should get progressively better. If they don't, then those weren't the real odds of success in the first place.