Copyrighting Public Space--Photography Forbidden

The Copyrighting of Public Space--Photography Forbidden
It has occurred that an artwork is displayed in a public space, but the public is told "photography is forbidden." Should we support the artist, or the shutter-bug? Libertarians (strongly) support property rights such as home-ownership, but (1) "intellectual property" is very different from real estate, and (2) when the real estate under my feet is public, can my viewing be considered private?

Regarding "intellectual property", here is the framework for argument:

Intellectual property springs into existence through the force of government; it is thoroughly abstract and would disappear in the absence of the threat of government coercion. In effect, government is a party to creating potential wealth for some exclusive individual. By comparison, if the government printed money and gave it to someone favored for political reasons, libertarians would clearly be in opposition, but the granting of intellectual property is (presumably) not automatically wealth, and the assignment of that property is not capricious. The property rights can only be assigned to the creator of the intellectual work. There is no wealth until the assignee finds customers willing to pay. (At least that's how it's supposed to happen.)

The purpose of intellectual property rights, granted
by the government, is to encourage production. The purpose
of a patent is to encourage an inventor to put his product on
the market. The patent is also intended to encourage innovators
to improve on the original, while respecting the rights of the
original inventor. Likewise, the purpose of a copyright is to
encourage publication, since the author is given an assurance
against theft. In other words, the reason the government
grants these special privileges is for the good of the society,
not for the good of the privilege holder. By granting a privilege
to the innovator, the government is encouraging the creation
of wealth for the society.

Beware, however, that intellectual property rights are a major intervention within the
free-market system. Currently, patents are being used for
the opposite of their intended purpose: Big companies are
patenting every silly thing, and then squashing small
competitors who do common sense development, since
it will inevitably run into one of these frivolous patents.
The result is less innovation, less product brought to market,
and less wealth for the society. Also, when an assignee "parks" on a patent, hoping to sue some more resourceful person who makes a success of a similar idea, that's also not helpful to society.

The specific question regarding "forbidden photography" is the application of copyright to prevent photographs of publicly viewable art, perhaps including when that art is on public land, and perhaps even including when that art was paid for in some part by public funds (i.e., government money; our money.) The last point, public funding, should probably be part of another discussion, since it doesn't really concern copyright.