"You can't leave him here!" Professor McGonagall cried. "They're the worst sort of muggles! Why don't you leave him with Lily's parents, they're..."
"Too old to have a baby running around the house." Dumbledore said, cutting her off. "And besides, I wouldn't leave Harry there if they weren't. Do you have any idea how annoying Satanists are? It's hard enough to get muggleborns to attend even after we assure them that we're not devil worshipers, and the minute one of them writes home about what their dormmate worships... And then there's the Fat Friar in my office every week on the dot, complaining about Black Masses in abandoned classrooms. And then there's the Christian, Jewish, and Muslim students who violently object to their presence in the castle..."
"But, every student has the right to worship or not worship as they choose, it's in the founding charter..." McGonagall objected.
"Only because half the Founders were Christian and the other half worshiped the Old Gods. If they'd known that that lot had gotten into the school..." Dumbledore said. "I've left a request that Petunia keep Harry from such disruptive influences in the letter I'm leaving with Harry, so it doesn't matter either way."
Several Hours Later:
Vernon Dursley had watched his wife read the letter that had come with the bundle on the doorstep with a steadily growing frown for the last two minutes. As he mustered up the courage to suggest to his wife that maybe it would be better if she read it later when she was feeling a little better, Petunia suddenly started laughing hysterically.
"What does it say Pet?" Vernon asked as he attempted to read the letter that had been left with his nephew over her shoulder.
"Nothing that really concerns you." Petunia said as she refolded the letter with a vindictive smile. "I think I'm going to be calling my parents."
Several Years Later:
"Hail Satan!" Harry called out as soon as the Sorting Hat was off his head and he was on his way to the Gryffindor table.
A responding "Hail Satan!" came from the Finch-Fletchley boy at the Hufflepuff table as a groan and a "Hail Satan!" came from the staff table.
Everyone turned to stare at Professor Flitwick.
"What?" he said. "Dumbledore wouldn't have had me supervising the Black Masses if he didn't mean for me to convert, and Lily was very persuasive."