Why Do Creationists Spend So Much Effort in Trying to Disprove Evolution?

Visit most creationist "research" institutes websites and you will find countless article attempting to debunk evolution. Why is this so? Evolution and creationism are not logical opposites. If evolution was disproved tomorrow that would not make creationism more valid. Why do they spend so much effort on pseudoscience that tries to disprove evolution instead of trying to find their own proof.