The Daleks were not created to be evil but merely to survive, Davros says so himself in Genesis. The Doctor interfering with their plans changed them by forcing them to upgrade and incorporate time travel into their design in order to fight a new enemy. Without this Time Lord interference they may never have learned of time travel and merely been content to conquer only the time they originally occupied. Its probable however that they would have learned of time travel when they needed to conquer Galifrey. One could say that its the Time Lords fault for exposing the Daleks to time travel before they needed to.