I think there's also the icky implication that the prejudice Severus dealt with, not being traditionally attractive or popular--even if it was for valid reasons--trumps the prejudice that Lily dealt with because she was "muggleborn" (a direct analogy for class and racial prejudice). So like, Lily should've just gotten over it and understood that it was so much harder for him, not being popular like she was!

Looks a lot like a group of people who are still bitter about not getting to eat at the "cool table" when they were in middle school.