Pornography is here to depict fantasy, and most things people don't or can't do in real life. Just like we can't all fuck Angelina Jolie, or give a girl a bukakke...some people have rape fantasies. A LOT of women have rape fantasies, and I'm sure as many men dream of dominating a woman in the same manner. IN MY OPINION, it is okay to portray rape in porn. Just like it's okay to portray bondage, domination, double penetration, gang-bangs, etc. I draw the line at child porn, but there are plenty of producers out there putting their models in pigtails and school-girl skirts.
Porn, like the regular film industry, is all about fantasy. And who are we, as producers, to judge what turns some people on? Esp. when that's how we pay our bills...