Look no further than the Boston Marathon bombing, Newtown, Aurora, the list unfortunately goes on. Many acts of terror are caused by Muslim extremists from outside of the country, but that's not always the case. Somebody shooting up a bunch of grade school children is a terrorist act, it doesn't matter who is responsible for it. We thankfully have done some things to lessen the frequency of such barbaric acts, but they still happen.
No, U.S. policies have not reduced the risk of terrorist acts against the United States. It is not U.S. policies that have prevented additional terrorist attacks. Rather, it is the weak infrastructure of terrorist organizations that have prevented another attack. Making the public take off their shoes before getting on an airplane does not prevent a person who wants to hurt Americans from doing so.