History shows us that the risk of the state being co-opted by killers is non-negligible. We can try to prevent authoritarian elements from gaining power, but don’t you think the Dutch in the 1930s felt the same?
We need to be very careful what sort of tools we make available to future iterations of the state, rather than thinking in terms of how much we trust the current iteration (“mass surveillance doesn’t bother me because it’s Obama and I trust him”).
We would like for a benevolent state to have the tools to carry out the services we enjoy, including security, but we should try not to give them too many things that could become effective totalitarian implements at the flip of a switch.
The mass surveillance apparatus is exactly such a thing.