"What do you need boy robes for?" inquires Madam Malkins.
"I'm sometimes a boy," the girl explains.
"What?"
"Look—"
"… I don't know how to say it without it all sounding ridiculous? They think wizards are inherently better than muggles, they think muggleborns come from bad backgrounds, so they don't like muggleborns because they think they're inferior?"
"Like I said I don't know how to say it without it being ridiculous? And I don't know, I don't think anyone's really looked into it."
"That was me trying to be ridiculous – they honestly think you have impure blood because you're from a muggle family, and muggles aren't magic so they don't have the 'right blood', but purebloods do, so they think you're not as good literally because your bloodline isn't magical."
"Well that's silly. If we are just as good at magic why do they think that?"
"Good luck. Might have to wait for some of the older generations to die out."
"If it's all the younger years it might not be all that much of a conspiracy. And I meant adults, anyway, not like sixth-years."
"But the younger years will become adults. And, like, if I convince all of them then that means all adults graduating Hogwarts will be good to go."