Yes they use our rights and freedom against us, in the hopes that our democracies will collapse. If we tighten all the rules, strip away people's privacy and install a police force with more power we end up living in totalitarian regimes, which is exactly how most terrorists would have it.
From democracy to dictatorship is a big move if you wish to do it in one step. But if you take many small steps you'll be there before you know it.
The chances of dying in a terror attack are still so small it's barely possible to put it in figures. I realise a terror threat to the US mainland is relatively new, but the way NOT to deal with it is by panicking and enforcing all sorts of totalitarian rules.
We've been facing terror threats in this country for centuries, you can't go about limiting your freedom and everything you've fought for because of a bunch of jackasses with bombs. Don't let them scare you into killing your system for god's sake. It's the single worst thing you could possibly do.