Why would anyone expect him to change anything?
Because it's socially unacceptable to desire to have sex with children. Regardless of what happens in reality.
Well, if everyone is horrified by the social unacceptability of his fantasy life, which they've set up airport scanners to test for, without any reference to what happens or might happen in reality, that puts a whole different light on the OP's thought experiment.
Would I choose to eliminate a part of my mind in exchange for greater social acceptability? Maybe, maybe not, I dunno... it depends on the benefits of social acceptability, I guess.
There's a recent science fiction story that I can't recall the name of, in which the narrator is traveling somewhere via plane, and the security check includes a brain scan for deviance. The narrator is a pedophile. Everyone who sees the results of the scan is horrified--not that he's a pedophile, but that his particular brain abnormality is easily fixed, so that means he's chosen to remain a pedophile. He's closely monitored, so he'll never be able to act on those desires, but he keeps them anyway, because that's part of who he is.
What would you do in his place?
In the language of good old-fashioned AI, his pedophilia is a goal or a terminal value. "Fixing" him means changing or erasing that value. People here sometimes say that a rational agent should never change its terminal values. (If one goal is unobtainable, the agent will simply not pursue that goal.) Why, then, can we imagine the man being tempted to do so? Would it be a failure of rationality?
If the answer is that one terminal value can rationally set a goal to change another terminal value, then either