"The wizards represent all that the true "muggle" most fears: They are plainly outcasts and comfortable with being so. Nothing is more unnerving to the truly conventional than the unashamed misfit!"
     -- J. K. Rowling, 
"Of Magic and Single Motherhood" (Interview with J. K. Rowling) by Margaret Weir ("Salon," March 31, 1999) (http://www.cesnur.org/recens/potter_022.htm)

"From the beginning of Philosopher’s Stone, prejudice is a very strong theme. It is plausible that Harry enters the world wide-eyed: everything will be wonderful and it’s the sort of place where injustices don’t happen. Then he finds out that it does happen and it’s a shock to him. He finds out that he is a half-blood: to a wizard like Lucius Malfoy, he will never be a true wizard, because his mother was of Muggle parentage. It’s a very important theme. "
     -- J. K. Rowling (Nr)

Prejudice against Muggles

• compared to the attitude of Arthur Weasley ("bless them")
• "Muggle-baiting" - the Shrinking Keys
• during the Voldemort years: Muggle killing and torturing
• at the Quidditch World Cup - Muggle torture, connected to Death Eaters

• Salazar Slytherin - argued with Godric Gryffindor about admitting Muggle-born students
• Lucius and Draco Malfoy
• Mr. Borgin
• Voldemort (as Tom Riddle) - carried on Salazar Slytherin's work

• House-Elves
• Goblins
• Giants
• Werewolves

• Vernon Dursley
• Japanese golfer joke, American plumber joke
• motocyclists
• anyone different, including the people in cloaks
• doesn't approve of imagination
• Gilderoy Lockhart
• ugly old Armenian warlock ("No dress sense at all.")
• witch with a harelip

• students of many ethnic backgrounds, accepted apparently without question
• girls play Quidditch (but not for Slytherin, interestingly enough)
• Hagrid's attitude toward foreign students, especially those from Durmstrang
• "The less you lot 'ave ter do with these foreigners, the happier yeh'll be. Yeh can trust any of 'em." (GF28)

• gives second chances
• Snape
• Hagrid
• accepts anyone
• Lupin, as a student and later as a professor
• various speeches connected to Triwizard Tournament
• his attitude 
• is not accepted by everyone (e.g. Lucius, Fudge)
• stark contrast to that of Vernon
• Vernon is the epitome of mundane-ness
• Dumbledore is the epitome of enlightened magic and the representative of Gryffindor
• "Albus Dumbledore didn't seem to realize that he had just arrived in a street where everything from his name to his boots was unwelcome." upon his arrival in Privet Drive, SS1