Because in one of the books one of the higher ranked odst's called John a freak, and one of the legends writers thought it would be nice to make all of them feel the same way. To be fair, 117 killed a bunch accidentally after augmentation. It's possible a few could have heard this story. So, basically, they shouldn't [i]all[/i] hate spartans, some just think that it's unfair that they have advantages they can't attain and aren't worthy of being called the unsc's best.