I'm not really a big fan of the whole pornography debate. But it illustrates a persistent problem in ethical discussions. When we approve or disapprove of an activity, we seem to have an innate tendency to relax our scientific and critical standards regarding purported science that confirms our position, and crank the skepticism up to 11 regarding purported science that disconfirms our position. To say that everyone has an "innate tendency" to do something is not, however, to say that everyone actually does it. I'm saying only what Feynmann said: You are the easiest person to fool; you have to make a conscious effort to not fool yourself. We must consciously work to counter our innate confirmation bias.
As best I can understand, the anti-pornography position is that pornography is inherently and specially exploitative. It is nonsense from this position, then, to invoke "volunteerism" as a justification for either pornography or many kinds of scientific studies of pornography and sexuality. In just the same sense, it is nonsense (under more widely accepted standards) to "volunteer" to sell your kidney to a stranger. Because selling your organs so obviously violates your material self-interest, we see your attempt to volunteer as merely a response to desperate exploitation. Again, in just the same sense, it is ethically unacceptable to volunteer to sell your children into slavery; we have a moral obligation to ameliorate the conditions that make such a choice thinkable.
I don't know that I agree, but as an ethical position it is definitely philosophically respectable. I'm all for choice, but circumstances do substantially affect the choices available to a person; I believe — unlike one of my instructors — that only a few, extraordinary people can individually choose their way out of poverty, exploitation and degradation. There are choices we cannot in good conscience ever ask a person to make. If they do make that choice, their circumstances are definitely fucked up, and caring and engaged human beings have a moral obligation to change the circumstances.
The conceptual and philosophical problem, however, comes when our notions of what is intrinsically good and bad come into conflict. Our tendency seems to be to move from an essentially "propagandistic" argument, an argument attempting to change the listener's beliefs about what is intrinsically good and bad, to an instrumental argument, an argument about whether the behavior in question causes conditions we all agree are good or bad. It's certainly possible that some behavior one finds intrinsically bad also has bad effects. But if you find some behavior intrinsically bad you ought to bring extra skepticism of arguments that confirm your position, and extra charitability to arguments that challenge your position. You have to actively and consciously counter your own bias.
It is definitely the case that people who are not generally skeptical are vastly more prone to giving in to confirmation bias. What creationists, abortion opponents, gay rights opponents, New Age woo-woo heads, Libertarians and others who are not generally skeptical accept as "good" science (and reject as "bad" science) is ridiculous to a neutral observer. Abortion causes breast cancer? Give me a fucking break. But people who are otherwise skeptical also fall into this trap. The tendency is both innate and strong; it's easy to let one's conscious skepticism relax or weaken.
If you have good science for the instrumental badness of some activity you consider intrinsically bad, by all means present it, but first bend over backwards to consciously make sure you're not fooling yourself. You should know in your bones that in such cases you're especially prone to confirmation bias. The junk science isn't persuasive; it appeals only to people who are already predisposed to your position. All it does is let you feel self-righteous; it lets you feel that your position is somehow "objectively" true. If that's what you want to do, well, it's a free country, but you will earn no respect from me or anyone else who values skepticism as both intrinsically and instrumentally good. (Of course if you don't want my respect, you're under no obligation to earn it, but you do have to earn my respect to obtain my cooperation. Votes do occasionally matter.)
Many cases for the intrinsic value of activities, irrespective of their instrumental consequences, stand on their own. You could make a completely airtight economic case for the economic value of selling organs; you will not budge a micrometer that selling one's organs is intrinsically bad. And my position will stay firm not because it is "dogmatic" but because it is not based on the instrumental value.
If you believe some activity is intrinsically bad, and some people are apparently choosing to do it anyway (or at least they are not being actively "gun to the head" coerced), then the only logical conclusion is that some element of circumstances is forcing them to a desperate pseudo-choice. This conclusion suggests that ameliorating the conditions that make the choice immediately plausible is the best way to reduce or eliminate the activity. If abortion is bad, make sure that women only get pregnant when they want to be pregnant. Duh. If selling one's organs is bad, make sure that people aren't so desperately poor that they need to sell their organs to survive with what's left. And if pornography is bad, make sure women have realistic economic alternatives.
Sometimes you can affect the "demand" side of the equation, but this approach always leaves an uncomfortable moral choice. It is, for example, relatively easy to make sure that the transplant infrastructure does not perform paid transplants, and we actually do so. But this approach entails that there are some poor people who will die who would otherwise have chosen to sell their organs. Similarly, if most women who "choose" to perform in pornography are forced to do so because of dire economic circumstances, if they are faced with the choice of pornography or starvation, then eliminating pornography entails those women will starve. I want to be perfectly clear: I am not arguing here either for the selling of organs or the permission of pornography. I am making much a narrower case: Simply removing the a bad choice does not resolve the underlying circumstances that make the choice plausible.
That's fundamentally why I'm a communist. I see a lot of bad shit going on, and hey, pornography might be among that bad shit. If so, then we have common cause: most of the bad shit in this world is caused by the exploitation of labor or the direct effects of that exploitation. Get rid of exploitation and you'll solve a whole host of problems.