Three things are wrong with this statement. Allow me to correct you since you're wholly uninformed. We didn't stop those extremists because we created those extremists. From before the Iran/Contra scandal to the Mujahideen to the Taliban which all birthed/fractured into ISIS/ISIL and Al Queda... America had a hand in all of that. So creating them is even worse than stopping them in my book.
We do not live in a democracy in the US. This is a democratic republic, which is not a pure form of democracy. Only saving grace is that we do elect by majority rule - but it's not a pure democracy.
Sigh. I'm being reduced to 7th grade US Politics now. Hey!... look above. Third point... I did get out of it. Have fun - read more. It's fundamental.