I used to think that way, too. Having been raised and educated in a conservative Catholic school, I have been brainwashed into believing that the Catholic religion is the only true and correct one.
We were taught, during that time anyway, that “outside the Catholic faith there is no salvation.” We were also forbidden to visit or attend non-Catholic churches or services. I also remember that in our theology class, other religions like Buddhism, Hinduism and Taoism were considered “adversaries” of the Catholic religion.