Why do people make it seem that people who go to church often are automatically nice people?

I believe in God. I am Catholic. I don't go to church often and nothing is wrong with going to church often but going to church often doesn't mean you are automatically a wonderful person. I have known so many people that go to church often yet are racists, take advantage of people, etc. Both Christians and Catholics.
Why do people make it seem that people who go to church often are automatically nice people?
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