In John Bad Elk vs United States, the Supreme Court found John not guilty for killing a police officer who was trying to arrest him falsely. As you say, killing other Americans is not something most anyone would like to talk about, for any reason. However, there may come the day where just that is necessary to defend our freedom. We are not immune. History has not changed the nature of human kind to tyrannize one another. It would be an awful thing and something not done for "transient" reasons. In order to follow our forefathers, it would take a long string of abuses.