I try to avoid what I think of as the catholic fallacy. The term is inspired by—but not a comment on—the Catholic Church, as it's a very human error. Hence I didn't capitalize. (More on the name in a moment. Maybe you can think of a better one! Also, it's possible I read this phrase somewhere, but Google turns up nothing.)

The error is in confusing the implications (or possible implications or even misinterpretations) of a statement with the statement. Referring to the Catholic Church might help our brain tissue hook into the idea's kernel, by way of the Church's historic stance that the masses can't handle the truth (given the sparsity of education back then, this makes some sense), and the appointment of authorities to filter it for them. "The Bible is the truth but we can't really trust you to understand it, so you need us to explain it. And actually, go ahead and listen to us whenever you're in doubt." [Offensive continuation: "Also, do what we say or you'll burn in Hell. Hey, don't shoot the messenger. We didn't make the rules! God loves you infinitely; it's all for your own good. Oh yes, absolutely. Even eternal 'torture,' as you put it. That doesn't make sense? It doesn't have to make sense! The ego of thinking it should make sense! Shame on you!"]

The mental health and mass shooter debate is a good example of this "catholic fallacy."

That is, when someone picks up a gun and shoots themselves in the head, we all know that's a mental health issue.

When a person picks up a gun and shoots someone else in the head—someone innocent who really didn't deserve it and had no choice in the matter—this should, by most any measure, be an even worse mental health issue. (If the person then shoots themselves in the head, it seems unambiguous.)

Yet we can't trust you with the truth, so we're going to say it isn't a mental health issue.

The fact most mass shooters have not been diagnosed with a condition does not prove that they had none. How many people go undiagnosed? And how many conditions haven't been adequately named, described, or understood yet? Here the eventual behavior strongly suggests disorder. If going out in a blaze of fury killing as many people as possible for no reason isn't "insane," what is?

The fact OCD (etc, etc, etc) has nothing to do with shooting people does not prove that mass shooting has nothing to do with mental health. (It doesn't even particularly suggest that. Many mental health issues are drastically different.)

I understand the social and legal considerations (the need to avoid unfair and damaging stigma and prejudice, or on the other end, to avoid encouraging or excusing violence), but those do not and cannot replace science. Allowing them to would be an example of what I'm calling "the catholic fallacy." Brain tissue seems to produce, and certainly mediates, behavior. Diseases of behavior fall under psychology, neurology, and mental health.

 

To give a different example of "the catholic fallacy," if you're late for work and spent 30 minutes in a traffic jam when usually it's 10 minutes in a traffic jam, then that is a factor in your lateness, regardless of whether someone feels you ought to be allowed to use it as an excuse or not. To blot out the traffic as "just an excuse" and somehow not real or worthy of any consideration is "the catholic fallacy," because objectively it was a factor. Its existence and its implications should not be confused for each other. Maybe you could have left earlier. Maybe you could have checked Google to see traffic conditions. Maybe you could have called ahead. Maybe maybe maybe, yes, but it was a factor, and "excuse" or "not an excuse" on some very basic level ceases to carry relevance and becomes a matter of opinion. Science is concerned with facts and factors, not "should" or "excuse." To confuse the two areas is the catholic fallacy.

To put all this in a nutshell—to sum the fallacy up—it's "You can't handle the truth; therefore it isn't true." Or "Someone else might get the wrong idea; therefore I will insist the truth isn't true and yell at people who speak it." Or "This is a possibility for all I know, but I don't like the way it looks to say so, so I will deny it and believe my denial."

"Catholic" means "universal," so I'm generalizing from that meaning and not trying to grind an axe with religion (the historic inconsistency I pointed out above seems fair to mention in passing, but I'm not judging people themselves for believing things that I think don't make sense). Again, maybe you have a better term. This is related to "political correctness" or "hypercorrectness" but need not involve either. It homes in on a specific and common logical error. "Out of the universe of all people, someone's gonna misunderstand." And that's true. But it doesn't change the truth.