What's discouraging terrorism is the US's overreaction outside the US. It's become very clear to terrorist organizations that if they attack the US, the US is going to hit back, even if it's insanely expensive and causes collateral damage. The people in charge, and many people around them, end up dead.
Remember ISIS, the Islamic State? ISIS is down to 1.5 square miles, surrounded, and everybody but the most fanatical fighters is surrendering. The holdouts have days to live.
We don't need more Big Brother.