Openness means the simple availability of the resource. All the resource. When someone violates openness, the rent is obvious. Users route around it, almost automatically, and condemn those who violate the principle.
This is an essential element in the free competition open source brings with it. If Microsoft had the power to stop you from gaining access to Linux resources, Linux would not exist.
But it goes well beyond that. Openness is the value which allows any small project to freely compete with any large project, or any proprietary offering as well. If you can't reach it, it is not there.
Openness, as a value, is far more controversial than consensus or transparency, because its impact is double-edged.
Openness enables free access to evil as well as to good. It depends for its maintenance on the goodwill and maturity of the user community.
This is often too much to ask, even in the best of households. It conflicts with the need for security, with the desire to protect those who are near to us, what we consider our property or even our national interest.
So openness is routinely violated. In censorware. Through corporate security. By government firewalls. Through monopoly. Users who believe in the value route around these difficulties, but casual users are also routinely denied access to what their betters choose to forbid.
This, too, is double-edged. We wish to protect kids from violence and pornography. But governments seek protection from extremism and crime. Religion seeks protection from blasphemy. Private property rights also interfere with this principle.
Yet the principle remains, as an ideal. We know how censorship can be a slippery slope. Protect us from porn and you may ban political discussion. Protecting copyright can also mean protecting monopoly.
These debates will continue, both in what Lawrence Lessig calls the East Coast Law of political choice and the West Coast Law of computer code. And those on the losing side of the openness debate, regardless of motive, will continue seeking ways to route around the censors.
On behalf of this most controversial of open source values.