sometimes i think it's as simple as this: i cannot believe in creationism because there is no way i can believe that we have evolved to where we are on purpose and that God's plan actually meant to include such stellar human achievements as the show Trading Spouses: Meet Your New Mommy.
God: oh yeah, totally. i totally created man and woman so that like, you could discover fire and build yourself some civilization and create art and learn science and eventually, with lots of guidance from Me, grow to provide all humankind with silly string and microwave popcorn. yes, that is most definitely My Plan.
whereas the theory of evolution allows for the idea that nature is messy and not always super efficient and thus has built-in explanations for things that are clearly evolutionarily awry, such as (in particular) the people i have to ride the bus with.