The problem I see with creationism is that the evidence for it is more a lack of evidence for something else.
My understanding is that a lot of it is based upon simple logic. For example, I've heard this argument before:
If we were to visit a part of Mars we haven't yet seen before (with a robot or a human, it doesn't matter) and we were to see a large glass dome on the surface of Mars, we'd be intrigued for sure. Upon further inspection, inside this dome is not only breathable atmosphere, but it is teeming with all sorts of life very similar (or perhaps exactly the same) as life on Earth. As we investigate, we discover that there are various control mechanisms inside which can set the conditions to an amazingly wide variety of potential settings, but every single one is PERFECTLY adjusted to allow the life inside the dome to exist, and if even one of those settings was off a small amount, there would be no life there.
What is the most logical conclusion as to how the dome and the life inside came to be there? Did the dome come about over a long period of time and create perfect conditions and the life inside simply evolved into what it was over more time? Or is it more logical to think an intelligent creator and designer of some sort created the dome and the conditions inside with the expressed purpose and intent that life could thrive there?
and that brings me back to my point from earlier, who created God? If everything must have a creator, than God must have been created by something?
Most (not all) creationists believe in some form of the kalam argument, even if they don't know it or what it means. It essentially states that "everything which begins to exist has a cause", and it's a logical premise accepted by many scientists (again, not all).
God is said to be outside the realms of space and time. Following the kalam argument, God did not have a beginning and therefore did not need to have a cause or creator.
Just like those that believe God did everything believe God has always been there. There doesn't actually have to be a beginning an end.
The Big Bang Theory supports the idea the universe had a definitive beginning. If that is true (again, it's a theory, not a fact), then following the kalam argument, it also has a cause, and many believe that cause was God (or another intelligent creator).