In Life of Christ, while discussing the temptation in the desert, Sheen writes:
Very few people believe in the devil these days, which suits the devil very well. He is always helping to circulate the news of his own death. The essence of God is existence, and he defines himself as: “I am Who am.” The essence of the devil is the lie, and he defines himself as: “I am who am not.” Satan has very little trouble with those who do not believe in him; they are already on his side.
Even though the Bible, the Cathechism, and Pope Francis mention him frequently, I would guess a not-small proportion of Catholics follow the standard cultural non-belief in the devil. It wouldn’t seem to require much philosophical heavy lifting, though, to believe in the devil or at least in the “spirit of the antichrist.” Even if you didn’t believe in angels (regular or fallen), the fact of an all-good God who creates rational beings with free will suggests that some of these beings will turn from Him, some permanently so. Even eternal misery loves company, so it’s no surprise that those who have chosen to turn away from God would want others to follow, especially if that initial turn was motivated by pride.
The devil certainly is powerful and a deceiver, but there probably is a danger of believing he has more power than he actually has. Fr. Vincent Serpa, on a Catholic Answers Live show, told a caller not to worry about the devil; put all your thought on Christ. From the temptation in the desert (the scene about which Sheen is commenting), to the passion and resurrection, to the defeat of the dragon in Revelation, we see time and again that the devil is a loser. Our side wins. We just have to make sure we stay on our side. Thankfully, the Church provides sufficient means for us to do just that.