Daleks have only one purpose in life: to expunge every other life form from existence. Tolerance isn’t something they’re known for. Anything not a Dalek is seen as inferior, an intolerable stain on the fabric of the universe, something that must be removed in order to restore universal purity.
They care nothing for other species’ right to life, have no interest in natural evolution, or the many amazing discoveries that have been made by non-Daleks. Art and music and culture are things they don’t understand. They see themselves as the pinnacle of creation.
The Doctor knows they must be stopped.