One condition for something to count as science is falsifiability. In other words, it has to be open to criticism. If something can't be criticized, if it can't be attacked, then it isn't science. Creationism isn't science because it can't be criticized. It belongs to the realm of belief, not science.
If something can be criticized but nobody has yet been able to do so, we provisionally assume it to be true. According to the 린디 효과, if something has survived a great deal of criticism and is still standing, it is likely to be true. There is an English saying for this: If it ain't broken, don't fix it.