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 citizen

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.