Logical inconsistencies.
"Excuse me, Professor, I have been told that Hogwarts is the safest place in Britain.
"Yes, Harry, that's perfectly true," the headmaster's eyes twinkled.
"Well, I wrote to Salem, Beauxbatons and Durmstrang, and none of them has ever had an incident like a troll roaming the corridors, so if Hogwarts is the safest place in Britain, it's not safe enough and I'm moving abroard."
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"So let me get this straight, Professor McGonagall. I am being punished for being out of my bed after curfew, because this is detrimental to my health as a growing Wizard?"
"Yes, that is so, Mr. Potter."
"So I am being punished by being kept from my bed after curfew and sent into a dangerous environment. In what way is protecting my health covered by this?"
"Weel, it's a detention..."
"A detention making me do what I was being punished for? In what way is this logical? I refuse this detention on grounds that it is contrary to proper rules of health and safety."
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"So the Philosopher's Stone can restore Voldemort and it's hidden behind a three headed dog and other intricate defences, right, Hermione?"
"Yes, Harry, I told you. "
"And if three firsties were able to get through those defences don't you think Voldemort's adult agent would already have done so? Either it's well protected by the headmaster and we have no business risking our lives looking for it, or it's so badly hidden that we might as well flee the country because Voldemort is going to win, as plainly Dumbldore is too senile to oppose him."
"Dumbledore isn't senile! He's a great man!" shouted Ron.
"When you put it that way ..." said Hermione sheepishly.
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