I agree that Peter Parker should stay as he's always been depicted. I'm not for swapping the ethnicity of established characters as I think it's a knee jerk move. But introducing Miles Morales to the main Marvel U is not changing Peter, it's introducing a different Spider-Man - one that can co-exist with old-school Spidey. Peter can still be his own man and it harms nothing to allow a character with a different ethnic background to embody their own version of Spidey.