Change My Mind

Neville was comedic relief for a majority of the films and the plot would've gone as planned even without him. Luna deserves someone who had a bigger role in the series. And I am almost totally convinced she's into girls.
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Fred and George shouldn't have been twins. Change My Mind.

Them being twins, especially identical twins, creates a bond between them. If it wasn’t for that bond, they wouldn’t have founded a joke shop together, which wouldn’t give Harry something to spend his Triwizard Tournament winnings on. Also, Harry got some items from the Weasleys’ Wizard Wheezes that we’re important later.

Voldemort should have just kidnapped Harry and raised him as a Death Eater. Change My Mind.

Voldemort wanted Harry dead for the same reason that Cronus wanted all of his sons dead. Because Zeus would become more powerful than him and defeat him. It's the same thing for Harry with Voldemort.
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Ginny shouldn't be with Harry. Change My Mind.

Without Ginny being with Harry, he would have lost one of the key people in his life. No Albus Severus Potter, for one. The entire story of the Cursed Child negated.

Someone should have killed Percy when he went over to the Ministry.

I never read Cursed Child. Oops)

But Percy-- Idk, I agree XD. Ummmmmm, he's better than Umbridge?
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Voldemort should've been reformed like Anakin Skywalker/Darth Vader from Star Wars.

Doesn’t suit his personality, from everything we’ve learned about Voldemort from the books. It’d be like taking a super funny character who never takes anything seriously and then just all of a sudden they become super serious and solemn.

Dumbledore shouldn’t have raised Harry like a pig for slaughter. Change My Mind.

How else would he be determined enough to fight for his life and save Hogwarts and the Wizard World? (Even though I totally agree with you)
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At least one teacher should've walked into Moaning Mertle's bathroom while Ron, Hermione, and Harry were cooking up that spell in Chamber of Secrets. Change My Mind.

Yeah, umm... the teachers at Hogwarts weren't the best caretakers of children considering how many times they almost let one or several students die. Ex. Triwizard Tournament; most DADA teachers; dementors around the school; keeping dangerous items in the school; letting the students have murder weapons... XD

The teachers at Hogwarts weren't good caretakers of children. Change my mind.

Hagrid.
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Ron and Hermione shouldn't have gotten together.

Hermione will have gotten bored in a matter of weeks - plus, they grew up together. They probably view each other as siblings.
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Snape's redemption ark was poorly done, and his character has done to many atrocious things to deserve any sort of redemption anyway.