Uther hates magic because it killed his wife, sort of. Arthur was born of magic because Ygraine couldn't have a son; according to teh old religion when a life is created a life must be lost- Ygraine died, and Uther felt he'd been cheated. He decided magic must be evil.

I have no idea why Merlin wears a blue (or red) scarf. He just does XD

^ lol He just does

He wears the scarf because the all mighty costume director comanded it to be so. And its very useful, its also a bandage, rag, and potion applier

We also wears a red scarf. ;D And that's one reason why everyone loves him I guess. XD