I like watching anal sex, only when it is performed and filmed correctly. When there is any sign of pain/violence or some physiological unpleasant stuff and ugliness, I do not like it, as well as all other types of sex in porn.
But some girls have got such a dexterity, or even talent for anal sex, that it looks like lustful masterpiece when they take a cock up in the ass. It looks like some asses are really elastic, or well trained, or girls are just imitating pleasure so well - whatever the reason is, it still does look very sexy and stimulant. There are a lot of examples, I do not need to call the names, those who are fond of porn know them perfectly.
So, for me anal sex in porn is a good stuff, under certain conditions. When it looks like a girl taking it easily, with some sort of pleasure, willingly, and when the girl is young and beautiful, and her ass is clean - it is great! but anyways this is not necessarily so for me.
And going back to the question, why do some people "insult" stars who are not performing it... Well, I guess that it is simple reaction, like an irritation. When you want something, and do not get it, you might get angry. It all depends on your temperament.
As for me, I esteem and respect those who perform it, but do not request this from every girl.