In the case of land, there's an absolutely limited supply of land, and so I think it could be argued that, in balance, it's more important to make sure that limited supply is used effectively.
Gold, by itself, isn't actually very useful. If someone wants to hoard it, they'll increase the market price for it, and maybe luxuries like jewelry or electronics will be more expensive, but it won't affect much.
I'd actually argue that patents that aren't being used should be made public domain. There's only so many good ways of solving some problem, and if society is blocked off from using some or all of them, then society is that much worse off.
If used as intended, to protect the results of invention/research until a product is brought to market, a patent's downsides are outweighed by its benefits.
A wealth tax is an interesting idea. I have to wonder why it's so uncommon. I'd guess it's some combination of being hard to enforce and easy to move money around. Such a tax would trigger a flight of capital, something that can't happen with a tax on houses. And you can't audit people's mattresses very easily, so it would just encourage hoarding cash.
In a world where such a tax could be enforced and applied worldwide, it doesn't seem like a terrible idea. It shouldn't be very large, but it could have similar effects to property taxes.
On the other hand, we already effectively have such a tax, we just call it "inflation" and the tax rate isn't directly controlled by the government. Inflation has the same good effects I described for property taxes, in that it discourages hoarding and encourages putting money to work. (It has bad effects to, no doubt, so this isn't a total endorsement of inflation or anything.)
Yes, they are. (Particularly, they are intangible personal property.)
> They're a government-granted temporary monopoly.
All "property" is government-granted monopoly in the control/use of some thing (sometimes dependent on a grant from another private party, but still ultimately government granted), concrete or abstract. Some are temporary (this is true of real and tangible personal property, too), some are permanent.
> In the absence of government, there's still some notion of property, but no notion whatsoever of patents.
Outside of government/legality, there's certainly still some notion that things, concrete and abstract, can belong to certain people such that it is wrong to "steal" them, and that certainly includes ideas. The particular details and names of particular classes of property are, of course, products of people, over time, spending time teasing out vague notions into more detailed sets of rules -- which, in the case of property rights, is something that tends to happen in the context of government (not always by government, but you don't even have developed philosophy of property rights without government existing to create a stable enough society for people to spend time writing rather than defending their immediate personal possessions and survival necessities.)
Humans have an intrinsic idea of "property" that the legal idea is built upon. A two-year-old child understands the idea of "mine". People still own things when government is not present, they just have a harder time enforcing that ownership.
Patents, on the other hand, are an entirely governmental construct.
Edit: additionally, cash doesn't expire, while patents only last two decades.
To play the devil's advocate: Why stop at land? What about people who have gold under their mattress? Or perhaps (stick with me here) someone who owns the patents for a machine that he refuses to sell anything himself and forbids anyone else from selling anything remotely similar?
Also, I hear we pay farmers not to produce crops because we are afraid seasonal over-production could destabilize prices?