Photography and film, out of all the other artistic mediums, present to us the ultimate challenge of illusion. Because photography so closely, or so immediately, represents the physical, and film so closely, or so immediately, represents the physical and time, the spectre of illusion rises up unprecedented and multiplied, rather than recedes.
The greater the claim of the medium to representing instantaneously all aspects, the greater the danger of reducing that which is represented to object irrevocably, and the greater the danger of corrupting entirely, rather than in part.
Certain writers like to play this indifferentist game where they take the example of a person being sexually aroused and entertaining impure thoughts before a work of art that is not pornographic in any way, and then pit that example against the example of someone looking at hardcore photographic pornography without any sexual arousal whatsoever - both examples which can, and maybe do, exist.
I tell you one thing: though that person who fell into impure thoughts before some non-pornographic artwork has committed sin and needs to address seriously this issue, the person who has looked at hardcore porn without a whiff of sexual arousal has committed the greater sin, and has put his soul in the greater peril.