Actually, the Amish and Mennonite groups are supposed to be non-resistant. This is different from pacifism which allows you to be involved in the political world such as protests as long as you are not violent... think MLK Jr.
Non resistance comes from Jesus' words to resist not evil and to turn the other cheek. As a result, if an Amish man were involved in a scrap, he would not defend himself.
This also extends to the fact that these groups believe that they should not judge other people. If they were to fight, they would be saying that the opposing party is wrong. They also are C.Os, so that they want to make sure that they are leaving a consistent witness for the government to see.