Ever had someone answer with "just because" when asked the why of something? Children are noted for saying that; often, when asked WHY they did something wrong, that is what they say. Even adults tend to say that.
I submit that "just because" is not any kind of reason. It's simply a cop-out, a lame excuse, and a non-answer. If one is three years old, we'll look the other way or even smile at that answer, but if much older, "just because" doesn't cut it, people!