The argument isn't that meta-data can't be used to get a lot of information about someone. The argument is that in the U.S., meta-data isn't protected information. Call meta-data is not your information, but information the telephone company keeps about you. In the U.S., the 4th amendment does not protect those sorts of records: http://en.wikipedia.org/wiki/Smith_v._Maryland. Your cell phone, which you use voluntarily, gives the phone company tremendous information about you, and under U.S. law nothing keeps the government from getting that information from the phone company.
Does call meta-data give the government a lot of information? Yes. Does it give the government too much information? Quite possibly. But arguing shrilly about how collecting call meta-data is "illegal" is counter-productive. Maybe it should be illegal, but you can't start the process of making it so by proceeding from an incorrect premise. And you can't dismiss the goal of making it illegal, by arguing that the government is already ignoring the law, with reference to activity where the government is clearly attempting to stay within the law, even if it is pushing the boundaries as much as it can.
One is what the general public thinks about the importance of metadata; the OP shows that it is a bit more than some may think, so arguing about the legal aspects is a bit beside the point.
That said, if you want to argue the legality, it isn't that clear-cut, either. The problem is that while Smith v. Maryland may resolve the question of the constitutionality of the collection, it does not answer the question of its legality. In addition to a search or seizure being constitutional, there generally also needs to be a statute authorizing the search or seizure.
Unfortunately, whether there is such a statute is highly dubious. The leaked court order used an extremely suspect interpretation of section 215 of the Patriot Act to justify seizure of the phone records; which is what Senators Ron Wyden and Mark Udall kept pointing out. Seizure under the electronic surveillance provisions of 50 USC §1801 etc. does not solve the problem, either, because 50 USC §1801(n) defines "contents" for the purpose of electronic surveillance to include metadata. And seizure under the Pen Register Act would require the government to certify that the information obtained is likely to be relevant for an ongoing criminal investigation.
This means that while Congress could have authorized the NSA to collect the connection data in such a fashion without such a law being unconstitutional, it is at the very least questionable whether Congress actually did such a thing.
To put the link into perspective: That article stems from a debate around the German "Vorratsdatenspeicherung", an attempt to put law into place which forces telecommunication service providers to store metadata (of telephone calls and - technically curious - emails) for six months. Law enforcement would then be able to access metadata for such a timespan. Law enforcement could query for all available data before that law was discussed, but the data wasn't necessarily available.
FWIW, the law was put into place and revoked by the German constitutional court, the "Bundesverfassungsgericht".
Of course, German data privacy law works a bit differently, too. Metadata is covered, as long as it points (possibly indirectly) to natural persons. As long as the data isn't needed for any purpose covered by the business it stems for (as when the telephone bill is over the dispute deadlines), it has to be deleted.
The whole debate is about 5-3 years old here in Germany.
I don't think the argument is whether metadata is "protected."
I think that the argument is that the US is collecting whatever they want even on lawful citizens, not being forthcoming, and arguing its all legal whether it is or isn't.
Also - your notion that something not explicitly "protected" is fair game scares me.
Totally agreed. The law should reflect our morals. But we judge the legality of an action by the law, not our morals.
Moreover, the problem for privacy advocates is that the moral debate is even less clear than the legal one. Being able to declare the NSA's actions straight-up unconstitutional under the 4th amendment would avoid the mess of resorting to the democratic process to determine what the people, as a whole, really thought about surveillance.
Does call meta-data give the government a lot of information? Yes. Does it give the government too much information? Quite possibly. But arguing shrilly about how collecting call meta-data is "illegal" is counter-productive. Maybe it should be illegal, but you can't start the process of making it so by proceeding from an incorrect premise. And you can't dismiss the goal of making it illegal, by arguing that the government is already ignoring the law, with reference to activity where the government is clearly attempting to stay within the law, even if it is pushing the boundaries as much as it can.