When is a Religious Belief Delusional?

[Neo-Scholastic]

I say that triangularity would exist in potential even if the physical universe had never come into being to manifest objects that sentient organisms would recognize as triangular. Is my belief in triangularity wrong or delusional?

While how triangularity works is indeed a mystery, we have little doubt that triangularity in general exists, even if we don't understand it. It's an interesting question, but rather beside the point here. If by a mathematical "object" then you're referring to things like triangularity, or mathematical notions such as number, or mathematical objects like the Mandelbrot set, then you haven't aquitted your analogy. We don't think that any of these things "exist" in the same sense that we think God exists.

I appreciate your well thought-out post and wonder, to what extent we are now debating a matter of degrees rather than of kind.

My primary concern of this thread is what I believe to be a mischaracterization of religious beliefs, most specifically the existence of God, as delusional albeit in a weak sense. IMHO using terms like delusional is overly inflammatory because of the connotations with mental illness and/or deficiency. From your previous statements I take it that you are not opposed to using delusion to denote beliefs you consider more than simply mistaken, perhaps indicative of shirking some intellectual duty.

I agree that the remarkable correspondence between mathematics, which is wholly conceptual, and material reality is a deep mystery. No analogy is perfect. I was merely trying to set a minimum baseline example. It is not uncommon to believe that mathematical truths are discovered rather than invented. As such there is at a minimum a tacit acknowledgment of a metaphysical component to mathematics that cannot be reduced to the properties of physical objects and the interior physical reactions of particularly complex walking and squawking electrochemical reactions.

My basic position is that even a severely limited notion of Platonic Ideas is not different in kind from the notion of Divinity. Clearly, the Classical concept of God has be developed to a much greater degree, and perhaps in some sense is more speculative because it depends more on premises derived from personal experience than it does on self-evident axioms. The Christian conception of God further relies on the acceptance of the NT documents as historically grounded. It seems to me being less axiomatic does not itself indicate of a flawed application of anyone’s rational faculties or moral deficiency on the part of those holding religious views.

One, it [acceptance of mathematical truth] tends to demonstrate it's existence pragmatically, in ways that things like the sensus divinatis do not.

This depends on what you mean by pragmatic. If you mean only applicability to technical pursuits, then I would agree. The sensus divinatis will not reveal natural facts about the world. IMHO it is supremely useful with respect to navigating through the interior life of meaning, values, and motivations, even if when a secular person attributes it to animal instinct. Again, this is not a debate about which is the case; but rather, if it is ‘more than wrong’ to attribute such common and self-validating personal experiences to divinity instead of explaining them away or reducing them to natural causes.

…we don't hold these things to be true [math] in the same sense that many/most Christians hold God to be true -- there's nothing tentative or conceptual about God belief.

This may be your experience with believers. It is obvious that there are examples of stubborn people insisting on unsupported certainties of which statements like “The bible says it. I believe it. That settles it,” would be a good example. I have no truck with such as those. So I acknowledge that there is a point at which religious beliefs can become delusional but I have clearly indicated in the OP basic criteria believers could use for discerning them.

And that last point brings into focus the other side of the question, and that is the behavior of theists in relation to their beliefs. The confidence enjoyed by most theists is not abetted by the evidence for such beliefs, though I admit there is some, and depending, could consider it persuasive; theists aren't operating on the basis of evidence, their behavior is motivated by conviction which is only retroactively justified by appeals to evidence and argument.

You are entitled to your opinion but I respectfully disagree. That may be true of some religious people but that kind of ad hoc reasoning is not unique to religion. Moreover, I think you exaggerate the normal process by which acquire, adopt, and maintain their faith. There is little doubt that people raised in a faith tend to adopt that faith before they have thoroughly examined it. Yet, with maturity people do examine the reasons why they believe. Some will find those reasons sufficient. Some won’t. Others will lose faith and come back to it. In my own case, I have great but not compete confidence that God exists, firm but not absolute confidence in the general reliability of the Gospel accounts, and much less confidence in doctrines that depend on literal readings.

Which points to another area in which theist behavior is similar to delusion -- theists spend an inordinate amount of time rationalizing their beliefs…

Supplying reasons to a skeptical audience is not the same as rationalizing. Making a blanket statement like that is highly prejudicial.

I'm sure there are people who think that these ideas and forms exist in, essentially, a separate universe, mysteriously influencing this one, in a case that parallels that of belief in God. However, those are the exception, rather than the norm, whereas in religion, thinking such things is just par for the course, and believed with irrepressible certainty.

That there is an essentially separate universe of Forms and/or deities, is not the case I was trying to make at all.