Depending upon location, visiting prostitutes will either be dangerous, expensive, or both. Some of the arguments against prostitution apply to porn; some do not. Also, some people who shoot amateur porn are couples who would engage in sex with or without the camera. They may behave differently with the camera present, but they'd be sexually-active couples regardless.
Also, Mosaic law does not forbid prostitution; Proverbs makes clear that a man who fails to focus on finding and servicing his wife is a fool, but other than a general proscription against foolish behavior and a specific restriction against priests' daughters prostituting themselves, prostitution is permitted.
Paul's letters speak negatively of fornicators, but there is still a big difference between adultery (which society is called upon to forbid and punish) and fornication (which people should refrain from themselves, but which society as a whole is not called upon to forbid)
2. Many prostitutes/porn "actresses" were molested when young, are drug addicts, are sexually abused as part of their trade, and so on. By contributing to the porn industry, you are helping more young women enter the seamy world of sex for money.
Some are, some aren't. If adults voluntarily decides to enter the trade (or, for that matter, if both members of an adult couple decide they want the world to see their sexual relations), why should your judgement that they shouldn't override their judgement to do so?
3. The only reason porn is everywhere is because Larry Flynt and other scum teamed up with the ACLU to force porn on every community in the nation. If the states still had any states' rights, local communities and states could define their own standards. So liber(al)tarians sqwaking about "nanny state" should shut up - it's the ultimate "Big Daddy" state forcing immorality on everyone, thanks to the ACLU and pornographers.
Technology makes it unstoppable, regardless of what the laws say.
4. Since porn is so easily availabe, more and more kids are seeing it at younger and younger ages. Okay, so parents should control their kids. Practically speaking, the only way to completely protect your kids is getting harder and harder - can't even let them loose at the library or go to other peoples' houses. This argument is like saying that people can live at the town dump and have no rats or flies. You can keep your own house clean but if you live surrounded by filth the rats and flies will come in anyway.
The world is full of nasty things. It's no longer possible to shelter children from all the bad things; it is therefore necessary to immunize them. Teach children properly and an occasional porno spam won't hurt them.
5. Since porn is by nature not really satisfying, the bar has to be lowered more and more so people can get a "thrill". So porn gets weirder and weirder - S&M, tortures, animals, children, and so on. Now pornographers are recruiting kids via places like MySpace.
What portion of users "escalate"? My impression is that by far the most popular types of porn involve either women showing themselves off to the viewer, or heterosexual couples engaging in reasonably-normal sexual activities. Nastier stuff exists, but I doubt that it's really as popular.
6. There is a connection between pornography and sex crimes, no matter how much porn supporters pretend there isn't.
Nearly anyone who would be predisposed to commit sex crimes would be predisposed to seek sexual gratification by any easy method they could. So it would be surprising if very many sex criminals didn't use porn. What studies show a relationship between porn use and sex crimes beyond that obvious one?
7. Men who watch porn a lot have a more difficult time relating in a realistic and close way with the real women in their lives. Focusing on sex acts with strangers via media is a sickness, it is not healthy, and if anyone wants to say this is not true, ask any woman whose husband, boyfriend, or fiance has a porn fixation and ask her if she is fine with it.
Men men use porn because they have a difficult time relating in a realistic and close way with real women. Using porn probably doesn't help their condition, but it isn't the cause. To be sure, there are some men who would rather look at pictures of naked strangers than at a real live woman, and I'll admit I don't really understand that, but I would expect most men would rather look at a real live woman if one is available than look at porn, even if they'd rather look at porn than look at nothing.
8. Anything that helps undermines families undermines everyone.
I'd put pornography pretty far down on the list of things that undermine families. Porn is a symptom more than a cause; attempts to attack symtoms of social problems tend to backfire and produce more social problems.
If I had to teach my religious ed my view of why porn is wrong, here's one way I would do so:
Have you ever hung out with somebody, gone to their house because they had a pool, or a plasma tv, or maybe let them buy you stuff but you weren't really their friend? You didn't really like them, and, well, basically you were using them? You got your kicks and had some fun but it was phony and fake, wasn't it. Because it wasn't borne out of true friendship and it demeaned the person you used, but it also demeaned you, too. And it would be hard to put your finger on it, but you know you felt it was wrong.
Porn's like that, too. You are using somebody for your own private kicks; they aren't really yours; and you kind of feel demeaned for doing it.
Only God can give you the person to enjoy in an intimate way. He gives it to you in trust: it's marriage. Other than that person, nobody else belongs to you in that way.
V's wife.