This is where we must fight them.
We also must realize that what we put into our minds comes out in our thoughts and actions. When we look at porn, our mind takes it in, processes it and then takes the info to the next logical step.
Same as when we read something and it brings up a question in another area, we follow that and we eventually may find a new hobby.
Pornography does nothing but debase human sexual drives to the mere sexual stimulation and fantasies. These fantasies then take the mind and seek to act out. It is a devaluation of men, women, children and the sex drive to the lowest common denominator - sexual pleasure. It does not build up, it does not respect person, it does nothing but debase to the lowest level - the mere animal instincts.
This is the danger of pornography - it dehumanizes man as shown in the subjects of pornography.
With what ammo though? If you take God and His morality out of the equation, who are we to say that treating sex as a recreational activity to be shared with whoever as long as "consentual" is wrong? By that standard, I would also agree that many children that engaged in sexual activity with adults weren't harmed.