This is a really key point. Obama and Cameron are telling us that it's ok to let them snoop on all our private communications because we can trust them and they can protect us. Even if we can trust them, they can't protect us. Also, who knows about the next president of the USA, or the next UK Prime Minister? What if we get another Nixon or worse? These things have happened and will happen again.

Beyond that, by saying it's ok for governments to snoop on private communications, it's normalising that same behaviour by China, Russia, Saudi Arabia, etc, etc. It's not good enough to say that it's alright for the West to do it because they are good guys and not ok for despotic regimes to do it because they are bad guys. It's a matter of principle that it's wrong for everyone to do it.

That is the only way to set a standard and hold every government to it. We should figure out what line in terms of privacy and respect for personal rights we would like China, Russia, etc to abide by. It's only ok for our governments to do things that we would accept as being legitimate for those governments to do. That is the only way to normalise respect for the individual and protect our personal freedoms in the long term.