Looking at these definitions, it's pretty obvious what the one difference is between pornography and erotica. Porn actually tries to turn you on. Without knowing the intent of the creators, there's basically only one way that you can distinguish the difference between the two (which, in some areas, is a difference that could land you in jail), and that's if it actually turns you on.
Bringing up this issue is important, because there is a current in feminist thought that wishes to create a much stronger divide between these two things. Gloria Steinem's 1977 essay "Pornography vs. Erotica" does its very best to segregate pornography and erotica by the way that power was used in the material (and goes on to make some horribly ill-researched statements about S&M and snuff films).
This type of divide, however, is seriously flawed. It is very much just a step away from the steretypical anti-feminist argument of "A picture of nude man on top of a nude woman is porn, a picture of a nude woman on top of a nude man is erotica." Also, in this age of the internet, when erotic material of nearly any fashion is avalible to anyone with the ability to type, such divisions become laughably pointless. Finally, the very fact that she wishes to create a new, softer label to allow certain types of pornography while maintaining the social (and potentially legal) stigma attached to porn creates a strong suspicion of her intent.
Those attempts at division aside, the problem still arises that there exists pornographic works who's focus is upon the unwilling degredation of its subjects. What can be done about that?
Well, I'd like to make my own catagorical division. Not between pornography and erotica, but instead, between good porn and bad porn. Instead of some form of stigma attached to works of a various nature, there should instead be a commonly-held set of standards for quality amoung the material. I believe that this will do much more good than any possible taboos, as it is allowing instead of restricting. I also believe that, with the removal of taboos and greater access to the material, these standards of quality will develop naturally in our society.
So, to those feminists who's sensibilities are offended by certain pornographic materials, here is my call to action. I say, create you own, better, pornography. Find pornography that doesn't offend your sensibilities, that is of a high quality and promote that rather than rail against the material that is devoid of quality. That is the way that we're going to be able to change things in the pornographic world, and make things better for all of us.