1.  Only attractive women get sexually assaulted.  This is all kinds of win, because you get a 3-for-1.  Pretend that rape is about sex and not power, diminish the victims credibility because you found an unflattering picture, and maybe even silence those who have self-image issues, from high school no less. Because we all know no one who was weak, geek, or unattractive has ever been picked on or assaulted - physically, verbally or sexually.

2.  Marginalize one bad thing by drawing equivalence to something else different and less egregious.  But it works because you play on the fear of PC overreaction.  And you get to call out a poster you don’t like by creating an illusion of hypocrisy.