We had a discussion about this before in 420's fair tax thread. I decided to start a new thread specifically devoted to this topic.
I finally finished reading
Progress and Poverty, and I'm even more convinced than I was before that geoism is completely compatible with libertarian moral views and necessary to create a truly just and free society.
George talked about the various forms on income secured through land ownership, which he described using the umbrella term "rent". He argues that rent always tends towards the highest point the economy can sustain. Unlike other goods, demand for land cannot be balanced out by increased production, so the price tends higher. Whenever society becomes richer, whether through technology, population, infrastructure, etc, land value rises enough to absorb the extra value in rent, so that labor gets little-no benefit from the increased wealth.
The rewards of labor and capital comes from the value they add to the economy. People can rightly claim ownership over these things, because people produce these things. If I want to use a machine, it is completely reasonable to pay the creator a fair price, because if he didn't exist I couldn't have that particular machine at any price. If I want to use land, well, if it weren't for the owner and those like him, I'd have it for free. It's almost a form of extortion to have to pay him to not prevent me from using the land.
Keep in mind we aren't talking about the value of improvements such as buildings. Some will object that even unimproved land gains value through human activity. This is true. However, it is not the activity of the owner. Land gains value from the surrounding community. Landholders collect revenue from surrounding businesses that they had nothing to do with. This is not to say that landowning is a risk-free enterprise, but when they do make money it's at the expense of others. Labor and business make their money by production of new goods, landowners simply leech off of them.
If you think about it, the tyranny of modern governments is based on control of land. Most governments exert force within their borders and take relatively little interest in what happens outside. Yet, "love it or leave it" is not an acceptable principle, because we need land to live on and live off of, and pretty much all of it is under the control some government or another. Why is it acceptable for individuals to practice this level of control if not governments?
More than once in the other thread the objection of scale was brought up. Private landowners do not generally control enough land to exert the kind of coercion that governments do. There are at least three problems with this. The first is that there is nothing, in theory, to prevent any individual from coming to possess as large a quantity of land as necessary. The second is that while an individual landowner may not control that much, landowners as a class can literally control an entire country, and exert their collective will on the landless as a class. The final problem is that pointing out that competition exists among landowners in no way justifies it on a moral basis. If it is wrong for one person to own all the land, how can it be less wrong for several people to each own a part of it?
Then there's the fact that much land has not followed an unbroken chain of voluntary transactions from its rightful owner under the homestead principle to its current possessor. People may object that these thefts happened long enough ago that they are irrelevant.
George discusses this issue in his book The Irish Land Question. Basically, his point was that while stealing an object is a one time thing, robbery of land is an ongoing process. The families who stole land centuries ago have collected rent ever since, and those from whom it was stolen have been obliged to pay. While we might overlook the robbery that occurred far enough in the past, the robbery of land never stops.
So, I think that the land value tax is both morally and practically necessary. While I believe in a free market of labor and capital, for an individual to claim ownership of land is an act of aggression against others who need that land to live. In order to gain exclusive possession, one must pay compensation to the community in the form of the land value tax, which may be divided up among the community. It's a clean solution to historical injustice and it helps ensure that everyone will get to keep the value of their labor rather than losing it to rent.