The NSA (or any other organization) is not an enduring omnipotent and benevolent being. The constitution restricts powers of government. Increasing amounts of power can be abused to increasing amounts of public damage. It is foolish to assume the good intentions of today cannot be exploited tomorrow
If you follow the law, you have nothing to hide. I, for one, am completely Ok with the government looking through my emails, and texts and shit because I've done nothing wrong, why would I care? It's not like they can publish them.