How does this work?
It's not like they can kidnap people on the street and force them to become Protestants or Evangelicals.
Some will rant and rave on television and radio, but that's nothing different. The rest will go on living their lives with their belief systems as usual.
It's happened in the past, actually! Religious aggression in the US usually doesn't involve force or cruelty these days, but usually marketing. Churches increase membership by offering services to people, in exchange for attendance.
Some academics have actually argued that the freedom of religion in the United States made the country so religious. Because various Protestant sects were competing for members, they offered different services. This is the most common type of religious aggression, because churches offering tons of services (in the 19th century, this would include social groups, sports for young men, dances for teenagers, music ensembles, and schooling) essentially rewarded people for their piety. The more you went to church, the more you were able to enjoy the secular aspects of church that were unlikely to be found elsewhere. In most small towns today, churches are the only places where live music happens, and are often the only significant meeting places.
Because most European countries had much less religious plurality, they enjoyed a slow decrease in religiousness. If your town has one church, the churchpeople have no motivation to provide better services. People would go to church for religious reasons, and then go elsewhere for musical, social, or athletic outlets. Even the small towns mentioned earlier tend to often have one or two churches, to cater to the slightly different Protestant sects in a community. All across the Midwest you'll find towns with three or four churches at an intersection, usually all Protestant. This was incredibly uncommon in Europe until the modern era.
Some people also believe that the World Wars were so sobering that they killed off most piety in Europe, but I think this is often exaggerated.
