There's not much to believe really, all evidence points to evolution. That's why it's a theory: all evidence we currently have supports it. You don't see any idiotic religious fanatic attacking the Theory of Relativity and claiming that gravity is caused by the weight of God's mercy and time dilation exists because God can't keep up with you when you're moving really really fast, or Kinetic Gas Theory by saying that all gases result from God's holy fart. Intelligent design's just another religious belief that's in line to get shot down by reason: 500 years ago people believed the Earth was only 4000 years old, in 1600 people believed the sun revolved around the Earth, in 1900 Lord Kelvin believed that there was nothing left to discover in the field of physics, and today some quaintly backward people believe that God created mankind in his image even if all evidence points to the contrary.