Covering for your deity.
Not everything about religion is bad. And, at the same time there are many ways in which I think religion is bad for you. There are obvious ones like feeling guilty about your life or understanding your fellow human beings according to an ancient text and their belief in it, rather than their humanity. There are many others, but I was just struck by a specific way. A way in which it really manifests as a mental illness.
Some people accept the deity’s will — the typical ‘everything happens for a reason’ faith. As silly as this notion is, it at least means that the person holding this belief accepts the reality in front of them, with the only cognitive challenge being figuring out, somewhere in the future, why something ‘needed’ to happen. This is usually quite easy in retrospect.
However, if you believe that your deity will never fail you and that you should be leading a charmed life as a result, then when reality strays from this expectation, you experience some significant cognitive dissonance. You have to spend mental energy building a version of reality where everything is fine, in order to cover for your deity’s shortcoming.
The further reality deviates from what you believe your life should be, the more energy you have to spend believing that your life is fine. The more that happens, the less energy you have available for the rest of your life.
Not only does this influence how you understand and relate to the world, it also limits the extent to which other people can interact with you. Since you are living in this make-believe world that you are constructing and maintaining at great mental cost, you live in a world that you don’t share with others.
While those around you have to deal with what life throws at them and grow as a result, you remain where you are, fighting to maintain your illusion.
In this way religion isn’t bad for you because it is hurting you day by day, but it is bad for you because it is isolating you from reality, and the people, around you.