The thing is, when you've had kind parents your entire life, good memories don't stand out as much as they would for people who didn't. Harry has plenty of memories strong enough for a Patronus because he's had a comparatively shitty life to give them contrast, whereas Hermione had a largely happy life (at least before coming to Hogwarts), which means she'd have a lot less contrast for the really powerful memories to stand out from.

 

I suppose that could be true. However I'm pretty sure the running idea is that the Death Eaters are unable to cast the Patronus (or pure-blood maniacs and Slytherins in general). I think this was used to show their lack of truly happy memories, and not of their abundance of them. Spell theory wise I personally wouldn't think have many would be a problem. It may just have been the wiki but the power of the patronus depends on how powerful the happy memory is. I would take this to mean she would have trouble finding the perfect one that can make one hundred dementors flee, but not casting a working one. Also...

Hi everyone. Typically the lurker type but when I do post I am prone to binges of rambling. Sorry in advance.

 

This. While I agree that the parents should know by a few books in that there are racist people in the wizarding world, all Hermione needs to do is downplay it, or say the teachers have it under control. With no input from other wizards and their only extended contact with the "muggle-loving" Weasleys, they are forced to choose between trusting their daughter (who is supposedly a teacher's pet and shows signs of a strong moral compass), or dashing her dreams of becoming a witch.