You think removal of a leg is always an intrinsically evil act of mutilation

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I don’t - what did I say to make you think I would?
You may not be clear on the distinction between a moral act and the object of a moral act.
So removing a leg is not “an intrinsically evil act of mutilation?” Then neither is killing someone by putting a bullet in them? It is merely an act of mutilation that is not intrinsically evil so therefore it could be allowed in self-defense. Is that your point? Anything - like killing someone in self-defense - is not intrinsically evil, just an act of mutilation.
This seems a rather bizarre notion. Name something, then, that is intrinsically evil according to you. We’ll see if we can make it acceptable as an act of mutilation that is not intrinsically evil. I confess, I cannot make a distinction other than to dismiss everything, formerly called evil, as merely a mutilation of the natural order and, therefore, not intrinsically evil.
Even torturing and carving up a human being is merely mutilation in this sense. Even the person doing the carving might claim the evil that exists in his soul is merely a mutilation of the form of his body and, therefore, not intrinsically evil.
I think this notion of yours leads to rather odd conclusions.
Evil, by definition, at least in the Catholic readings I have done is a “perversion” of the good - the natural form of created things that naturally are ordered towards their teleological end or purpose for which they were created. When “mutilation” hampers the achievement of that end, it is considered an evil. When the mutilation positively stops achievement of the end good it is an intrinsic evil.
I am open to learning new things, so please do explain what “intrinsic evil” is, what are some examples of it and why mere mutilations are not intrinsically evil. I simply don’t get your concept of evil and how it can make a viable distinction between “evil” and “intrinsic evil” with anything like a reasoned argument.
I do understand, for example, that the surgeon does not intend the evil of removing the leg but must accept it as an unwanted effect of saving the life of the patient, but merely to claim that losing a leg is not an intrinsic evil because it was not the intended end is merely to put another word on the distinction between evil intended and evil permitted, which I suspect is what you mean by intrinsic, i.e., intended, which isn’t the position of ethical philosophers as far as I can tell.