In the victimology literature, there is a term called "blaming the victim." This is a form of rationalization whereby the person doing harm attributes the harm done to the person harmed. In the paradigm example, a rapist may say that the person raped deserved what happened to her because of something she did or invited the rape because of the way she dressed.
In cases of adult/child sex, the adult almost never tells the child that there is something wrong with, something to feel guilty or ashamed about - what they do. They do tell about the need to keep the activity secret, but this is because other people have the misperception that the activity is wrong (something to feel guilty or ashamed about) and will hurt those who do these things - even though it is wrong to hurt those who do these things.
Granted, there are exceptions - and your words are fitting for those child abusers who use guilt and shame as a way of manipulating a child. (What would your mother think if she ever found out what you are doing?) But their justification with respect to these cases does not imply that they are justified in all cases.
There is another form of rationalization known in the victimology literature whereby the person doing harm rationalizes his behavior by blaming it on a third party. The terrorist holding hostages or who kill and wound innocent people (and place others in fear of being killed or wounded - no small cost in itself) blame the object of their hatred for this harm. "They made me do it. They left me no choice." The man who puts a gun to a hostage's head and shouts "If you don't back away, I'll kill her," blames the police for not backing away when he pulls the trigger.
The same pattern of rationalization exists in those cases where an arguer holds childrens' self-esteeme hostage as a way of controlling pedophiles. "Do as I say, pedophiles, or the children die." Otherwise, ut would be more appropriate to direct the comments (and to blame the harm on) those who say that the activity is wrong.
To see this, look at the claim under debate here - the claim that "adult child sexual activity is wrong." The person making this claim is caught in a circle. Why is it wrong? Because it is harmful. Why is it harmful? Because it is wrong. There is no justification in this. The child is taught two conflicting messages - the "it is wrong" message and the pedophile's "it is not wrong" message - the pedophile who points out that the "wrongfulness" ideology is logically flawed is correct - and thus not the one to be blamed if the child should, instead, come to accept the false and unjustified doctrine of "wrongfulness."
By analogy, consider a case where somebody gives a child a ring - a gift. Then another person then tells the child, "that ring contains an evil spirit which will drain your life energy away as you sleep. It will destroy you - corrupt your soul - darken and sully all that is good within you." Here, there is no difficulty seeing the person who makes these claims about the ring as being wrong. And if the child should later suffer a loss of trust, nightmares, anxiety, and similar psychological symptoms, we easily see it as sophomoric for the person to claim, "See, the ring did contain an evil spirit that corrupts the soul." Yet, when used against pedophiles, for some reason this fallacy is seen as valid.
The best reason for this that I can think of is that pedophiles are the victims of a prejudice that induces in people a desire to harm and control pedophiles. This prejudice provides people with an incentive to seek out rationalizations for acting on the prejudice. They need excuses for the harms that they inflict, and the "tainted ring" argument provides a very convenient excuse. In short, people are convinced by this fallacy because they want to be - because it fulfills a desire that they have (one that they acquired as a child listening to adults tell them that it is right and good to harm pedophiles).
I am not speaking here of an action chosen conciously. The rapist does not say, "hey, I need a good excuse to rape this woman and holding the way she dresses against her is a good excuse, so I'll use it." Neither do those who victimize pedophiles (and the child lovers of kind pedophiles) conciously choose to adopt fallacies like the type mentioned above. They accept the argument because they like the conclusion. The fact that children are harmed when they act on this desire does not bother them - not when it is so easy to blame the harm they do on their victims.
Phil an251400@anon.penet.fi