If 3 is true, the whole of clinical psychology would be doomed. It is like saying humans cannot apply human thought to explain what motivates nonhumans. Or that the thinking cannot apply thought to explain the behavior of inanimate matter. We can observe.

Also, if 2 is true then the whole of clinical psychology is doomed, for it has no way to differentiate between crazy and evil. The two are not synonymous, popular Hollywood depictions notwithstanding.

I don't know why it bothers me, but your point 1 shooting is a heinous crime, is not relevant to your conclusion of 4, which utilizes only point 2 and point 3.

@dsollen I think 1 interacts with 2 informally by qualifying what is meant by "heinous crime." Perhaps what is bothersome is that it is only informally linked to the argument but has a side effect of tying the question to a very politically charged current event. When I look at how 1 interacts with 2, 3, and 4, it seems like its intent is to sway the logical argument with external details which, in a perfect world, would not apply to the argument at all.

One problem lies in the definition of insane. What is insane? Or, conversely, what is sane?

There is no logic in this fallacy. 2 is clearly false. 3 is clearly false. You cannot draw a valid conclusion from two invalid propositions.

@MasonWheeler you do understand that evil is not actually a thing right?

Several structural and semantic problems at work here, outlined in comments and in answers below. But there are important ethics problems struggling to get out, laced with psychological factors. Accountability an issue here, social rule systems (aka laws!) and maybe suspension of reason due to irrationality of human emotions. Logic and fallacy never had a chance. Maybe too many problems at once?

@JamesRyan: Of course it is; don't be ridiculous.

@MasonWheeler I hope you are joking. Morality depends on point of view and societal custom, it isn't arbitrary. You have no chance in psychology if you impose your frame of reference rather then trying to understand the subject's.

@masonwheeler with crazy being one pattern of behaviors, and evil being a different pattern? Measures of evil definitely relative to changing social standards James, if that is your meaning? Evils of today were more acceptable 2000 years ago ..

@JamesRyan: The details of morality depend on point of view and societal custom, but that in no way means that evil "is not actually a thing" or that it cannot be defined objectively. It's actually very simple: to desire your own will to such a degree that you are willing to knowingly, deliberately cause harm to others in the course of seeking your interests--or to act on such a desire--is evil.

There are people in the world right now "shooting a bunch of people" with everyone around them finding it OK. Not heinous, or insane, or even evil.

@MasonWheeler no, that is not an accepted definition. The vast majority of people deliberately cause harm to others to get what they want to some extent and don't consider themselves evil. Secondly what is your definition harm, is it defined by the harmer or the harmee? Can someone who underestimates harm that they cause not be evil in your world? Thirdly at what point do you care about harm to not be evil, friends, same religeon/nationality, all people, all mammals, all animals, all living creatures? Literally can't avoid harming something even if it is bacteria, who draws that line?

@MasonWheeler and who says that putting your own desires first is wrong? That in itself is based on tradition. In nature you see examples both for and against, does that make animals that don't work in social groups evil? If animals are excused because of 'instinct' then why shouldn't people? It is a can of worms, certainly not simple.

@JamesRyan: I see what you did there. I provide an objective decision, and you immediately try to confuse things with a bunch of questions about what people (subjectively) consider or believe about themselves. That's the beauty of objectivity: it's not affected by such things. (Just look at the Flat Earth Society!) I don't have the formal training in logic or debate to name the fallacy there, but I know enough to know your "rebuttal" is completely invalid.

"Is Evil a Thing" feels like it should be a question of its own, if by some miracle it isn't already.

@MasonWheeler what you provided was itself only from your point of view. You were not being objective because morality is not a universal constant, it is entirely subjective. Calling your own point of view "the truth" is a common fundamental mistake.

@JamesRyan: Can you name any act or practice widely considered to be evil, where the objection to it is not rooted in the definition I gave?

@MasonWheeler I don't need to, there are a wide variety of examples that fit the definition you gave that no one considers evil!

@JamesRyan: Such as...?

@MasonWheeler putting people in prison

@JamesRyan: First... seriously? That's the example you give? If you think no one out there thinks that's morally wrong, you're simply not paying attention. Second, the practice of incarceration is generally not motivated by a desire to seek one's own interests--particularly as (in most jurisdictions at least) the person responsible for throwing someone in prison isn't and can't be the victim in the case in question--but by the desire to protect those who are not yet victims from becoming victims, or to protect those who are from being further victimized.

From headlines of the past few years, one might be persuaded to believe that point 2 only applies to white American males.