Cruelty to Fat People- Why is this acceptable?

In case you haven’t noticed, I do the Twitter thing. If you’re not familiar with Twitter, it’s a social media avenue that allows you to share your thoughts in 140 characters or less. One of the fun things to do on Twitter is to follow the trending topics. Trending topics are the things that are being talked about most in 140 characters or less. And this morning the top trending topic was #fatpeoplearesexier. Cool, I thought when I noticed it. I normally ignore the trending topics for the most part, but this one made me curious and I clicked on the hashtagged words to see what was being said.
I really wish I hadn’t. The majority of the comments were not only negative, but downright rude and hurtful. I find myself wondering why people felt that it was acceptable to speak about a section of the population in such a hateful way? Which was quickly followed by wondering why so many people have such negative feelings about their chubbier counterparts?
I find it hard to believe that these same people would feel it was ok to say such things about the color of someone’s skin, so why does a person’s size makes it ok to hate on them?
Is it because they erroneously have the idea that people are fat because they eat more than others? (Although what you eat contributes, it’s not the only contributing factor to being overweight. Many overweight people eat less or healthier than thin counterparts.) Is their own struggle to stay thin making them resentful of those that they believe aren’t trying? (yet another misconception) And why isn’t there public outrage when these type of responses happen? Why is it acceptable to hate fat people?