A lot of what happens on the Internet happens because of a simple principle: if it's online, we assume that it's permissible to access it. We take for granted the ability to link to and access page and other data on the web. Mash-ups are an example of applications that rely on this principle.

Wired magazine has an article explaining why this principle may be in danger.

In a few years, legal doctrines being aggressively pushed by corporations and law enforcement officials might prevent something cool and useful like this from ever happening again.

In a variety of cases, courts are holding that people can't access Internet computers without first getting authorization from the computer's owner. Judges are assuming that the public has no right to use unsecured computers connected to the Internet, and are requiring the public to get permission first.

For example, many ISPs and some prosecutors are arguing that it's a crime to use unsecured wireless access points without the explicit permission of the owner. Antispam crusaders advocate blocking any e-mails that haven't been whitelisted first. Airlines like American and auction sites like eBay -- which want customers to visit their websites, view their ads and "join the community" -- have won court injunctions against companies that collect price information on plane fares or auctions to help consumers comparison shop.

Under ancient legal theories like "trespass to chattels" and ill-advised modern laws like the federal Computer Fraud and Abuse Act and state computer crime statutes, courts are holding that if you don't have authorization, you can't access computers.

And if you can't access computers, you can't collect data about airfares, auctions or evacuees.

From Wired News: Open Internet, We Hardly Knew Ye
Referenced Fri Sep 16 2005 09:28:56 GMT-0600 (MDT)

I believe that much of the trouble comes from the metaphor we've used to describe the 'Net for so long: cyberspace. As Michael Swaine described in a recent column in Dr. Dobbs, cyberspace is a metaphor of place whereas the 'Net has increasingly come to be able information flows.

Technometria isn't about a "homepage" (another place metaphor)--it's an ever changing stream of information. Likewise, RSS, mash-ups, and Web services are about information flow.

Allowing people to block access to their public sites without prior explicit permission isn't analogous to allowing people to have privacy in their homes--even if the door's not locked. It's more like letting anyone with water rights permanently divert the water from the canal, or block their downstream neighbor from getting to the water. (I recognize this analogy may not translate if you've never lived in the rural west and had to take your turn at irrigating your yard or crops--still, I think it's apropos.)