Subject lines are clearly not needed for routing.
There's feature creep (a.k.a. slippery slope) at work even for metadata.
The set of metadata used in routing, aka the 'envelope', also contains a return path, which is (normally) used for things like submitting delivery failure reports.
As we've seen in recent commercial data breaches, the collection of a huge amount of data makes a tempting target. The potential abusers of that data, in this case, is not only identity thieves, but foreign governments and "rogue" US employees. Although I'm finding it hard to remember what "rogue" means anymore.
by saying "the executive spys on the public generally in a way that acquires only metadata", he's sticking to the facts as admitted so far by these liars.
however, given that the people who are telling us they only acquire metadata, having previously denied it, also tell us they are not performing mass surveillance, use weasel language such as "under this program", redefine words that have sensible meanings such as "collect", it's worth taking the time to criticize someone for repeating their party line.
That somebody has said something may be a fact, but the substance of the content of that speech is not a fact. We have as much evidence that what they say is true as we have evidence that idle speculations that don't contradict the known facts are true. None. None other than what Snowden hands us, rather, which tells us that they are not only willing to lie to us, but excited to come up with new ways to do it.
>If we're willing to speculate without any concern for concrete facts
To be clearer: I don't think that the government is particularly interested in my genome, therefore I don't believe that the government has analyzed my genome. There's no evidence that precognition exists, so I don't believe that there are psychics analyzing me for future crimes. The government is clearly interested in the content of all of my conversations and everything that I read. Let's talk about the possibilities of that, instead.
There are things that the NSA are doing and have done that will never be able to be verified. There are things that I am doing and have done that will never be able to be corroborated, and will leave no evidence. Operating as if that's not a possibility is a denial of reality. Allow the facts to remain indeterminate, rather than relying on the testimony of the accused because you're starving for facts.