Not sure her Sonic run has much to do with her size as it does her lack of humanity.
The comments about looks have bothered me each time, but only now chose to post on it because it seems to have gone over the top in frequency.
People who are obese, or unattractive, or lousy dressers, or having bad hair days aren't bad people because of their perceived lack of "good looks".
And good looking people can be absolutely horrific. Some in Hollywood are prime examples.
I just have a problem when we seem to equate the two (bad people are ugly, ugly people are bad).
That ain't real life.
KK, IMO, is a HORRIBLE person, BUT not due to anything other than her actions and attitude.
That being said, sometimes one's personality is a reflection of their self-esteem and how well they take care of themselves, which can affect behavior and their decision making. Still, doesn't necessarily make them bad people.