How is that different from standard encyclopedia practice? It at least initially appears that it's one of the few things standard encyclopedias do better than wikipedia.

I don't mean to overstate the reliability of suicide rates for happiness. A variety of factors may influence them. However, there are reasons to believe they correlate with happiness.

What is a good measure of happiness? Virtually all measures are deeply flawed, but the most reliable is probably: Intra-observer self-report in situations when signalling is unlikely. People are probably decent at knowing when they were happier or less happy within their own lives. Inter-observer reports are far harder to justify.

People report being happier when they live in places with adequate sunshine; inadequate sunshine correlates with increased suicide rates. People report being happier when they are not facing loss of job, public humiliation, divorce, and a number of other events; these events correlate with increase suicide rates. People report being happier when mental illness symptoms are reduced (particularly depression); people with mental illness (particularly depression) have a higher suicide rate.

Obviously, suicide rates are not a perfect proxy for happiness... but I cannot find a more reliable easily-measured statistic.

Surely suicide rate is a much more trustworthy marker for (un)happiness than "numerical response to a survey question". So it is our previous flimsy understandings of what areas are happy (based only on the highly suspect methodology of surveys) that is wiped out by the new data regarding suicide rates.

As gwern points out, divorce is a poor marker; suicide remains a useful marker because it is nearly-univerally forbidden.

What does it mean for modus ponens to "do worse" than something? It might "do badly" in virtue of there not being any relevant statements of the form "A" and "if A then B" lying around. That would hardly make MP "fallacious" though. It might be that by deducing "B" from "A" and "if A then B" we thereby deduce something false. But then either "A" or "if A then B" must have been false (or at least non-true), and it hardly counts against MP that it loses reliability when applied to non-true premises.

Well, look at the Problem of Identity. I start with an apple or a boat, and I brush molecules off the apple or replace the boards on the boat, and end up with something other than an apple or a boat. This shouldn't be a problem, except that I've got a big Modus Ponens chain (this is an apple; an apple with a molecule removed is still an apple) that fails when the chain gets long enough. To fix my problem, I've got to:

a. Say actually, there are almost no apples in the world. Modus Ponens rarely applies to the real world because almost no premises are perfectly true. When someone asks "is this delicious-looking fruit an apple", I have to say "Dunno, probably not."

b. Say actually, there are apples, and an apple missing a molecule remains an apple, and Modus Ponens works except in rare corner cases. And experience/tradition/etc can help us know where those corner cases are, so we can avoid mistakenly applying Modus Ponens when it will lead from correct premises to incorrect conclusions.

Here you're talking about Euclidean geometry as an empirical theory of space (or perhaps space-time), as opposed to Euclidean geometry as a branch of mathematics

Well, Euclidean geometry is extremely interesting because it works relatively well as a theory of space, without actually relying on empirical data.

Users of a language have to agree on the meanings of primitive words like 'and', 'if', 'then', or else they're just 'playing a different game'.

I hope that logic (like Euclidean geometry) is actually telling us something about the world, not just about the words/rules we started with. If modus ponens is purely a linguistic trick rather than a method of increasing our knowledge, then it's as useful as chess. I think it's far more useful, and lets us obtain better approximations of the actual world.

I think the village girl in New York example can actually be understood a step farther. She doesn't just need to look at the dresses - the catalogs in her village show what they look like and cost. She also needs to see what people in New York actually dress like, and how the dresses work for them on the street.

Just so, many people have presented ethical dilemmas that are not part of our everyday experiences. If we have a useful morality core, then it (like most other senses or heuristics) is useful only in the areas in which it's been trained. The village girl needs the street experience in NYC to make good purchases. So the two arbitrary sequences would have to be similar enough to the intuiter's actual experiences to be accurately compared to one another.

You are certainly at least partly right. But:

After all, "contraband" methods of persuasion are rarely punished

Contraband methods of persuasion are weakly punished, here and elsewhere, by means of public humiliation along with repudiation of the point trying to be made. Some people go so far as to give fallacious defenses of positions they hate (on anonymous forums) in order to weaken support for those positions. Interestingly, the contexts where we think logic is most important (like this site) are much less tolerant of fallacies than the contexts where we think logic is less important (politics or family dinner). So while I'd love to dismiss that cynical explanation, I can't quite so easily.

People often have conflicting intuitions, but there seems to be some hierarchy which tells which intuitions are more basic and thus to be preferred.

Actually, there is indeed such a hierarchy in moral reasoning, and it has been better studied/elucidated (by Kohlberg, Rest, et al) than logical reasoning has.

The whole point of the tiger/rock parable is that the testing has all been done in environments devoid of tigers.

Similarly, the mugger-avoidance strategies I could offer to User:perturbation are all 100% effective since I've never been mugged... but I have no idea whether the opposite strategy would have been equally effective.

All my answers to this are flawed. My best is: It's like Euclidean geometry: humans (and other species) are constructed in a way that Euclidean geometry fits fairly well. The formalized rules of Euclidean geometry match spacial reality even better than what we've evolved, so we prefer them... but they're similar enough to what we've evolved that we accept them rather than alternate geometries. Euclidean geometry isn't right - reality is more complex than any system of geometry - but the combination of "works well enough", "improves on our evolved heuristic", and "matches our evolved heuristic well enough" combine to give it a privileged place. Just so, that system of formal logic works well enough, improves on our evolved reasoning heuristics, and yet matches those heuristics well enough... so we give formal logic a privileged place. The privilege is sufficient that many believe logic is the basis of Truth, that many theists believe that even angels or deities cannot be both A and not-A, and that people who use fallacies to convince others of truths are frequently considered to be liars. This does not sufficiently satisfy me.

An alternate answer, that a believer in absolute morality or logic might like, is that logic actually deserves a higher place than Euclidean geometry. Where geometry can be tested and modified wherever the data support a modification, logic can't. No matter how many times our modus ponens does worse than an Appeal to Tradition or Ad Populum in some area of inquiry, we still don't say "ok, alter the rules of logic for this area of inquiry to make Ad Populum the correct method there and Modus Ponens the fallacious method there", we just question our premises, our methods of detection of answers, etc. So logic is special and is above the empirical method. I am unsatisfied by the above paragraph as well.

A third possibility is that it's not - it's just a code of conduct/signalling. We agree to only use logic to convince one another because it works well, because the use of other methods of persuasion can often be detected and punished, and because the people who can rely on logic rather than on other methods of persuasion are smarter and more trustworthy. In specific instances, logic might not be the best way to learn something or to convince others, but getting caught supporting or using contraband methods will be punished so we all use/support logic unless we're sure we can get away with the contraband. This is an unsatisfying explanation to me as well.