Hey there, kiddo! Sometimes people in the United States have been mean to Catholics just because they believe in things that are different than what other people believe in. This is called anti-Catholicism.
A long time ago, many people in the United States were Protestant, which means they believed in a different kind of Christianity than Catholics. Some of them didn't like Catholics because they thought that Catholics worshiped Mary and the saints instead of God, or because they believed that the Catholic Church was too powerful.
Sometimes, people did mean things to Catholics because of their religion. They might have said bad things about them or even hurt them. That's not okay, because everyone should be allowed to practice their own religion without fear.
But, over time, more and more people in the United States have learned to be tolerant and accepting of all different kinds of religions, including Catholicism. Today, there are many Catholics in the United States, and they are able to practice their religion freely and openly.