That's what you get when you take away the beauty of the mysticism of Christ and the Church (eg. the Sacraments) and reduce it to a diagramatic science, a set of beliefs. When one diagram seems better presented or more believable than another, you can easily switch sides.
Often I think that the trouble with a/theism in our culture is that a lot of people (on both sides) have an image or idea of God that is unbelievable in the first place. The divinity they think they are supposed to believe in is less like the dynamic mystery of the Trinity and more like Zeus, Santa Claus, or the Great Pumpkin.
To make matters worse, we are taught to disbelieve in spiritual realities from an early age. Simple, ordinary spiritual things like numbers are "just concepts." Sublime spiritual realities like love, freedom, and truth aren't "actually real." And yet people everywhere make the most important decisions of their lives in the pursuit of love and truth. People routinely die for the sake of freedom. It's quite an accomplishment, to have folks organize their lives around you, and even die for you, without being "real."