The title had me captivated. However:

This post could use some more exposition in between the quotes. When "parasite load" was mentioned, my immediate assumption was that this was a metaphorical usage referring to "parasitic" ideas or memes, and was quite confused when I encountered a discussion of skin infections and whatnot, suggesting that somehow the literal sense of biological parasites was intended. This was confusing because I wasn't expecting any connection between psychological personality traits such as openness on the one hand and susceptibility to infectious disease on the other. Maybe such a connection is well-known in some circles, but I was totally unprepared for it and it came across to me as a bizarrely privileged hypothesis. Some more emphatic exposition, saying in effect "yes reader, I really do intend to relate the personality trait of openness to the medical phenomenon of infectious diseases" would have been helpful.

What kind of 'morality' are we talking about here? If we're talking about actual systems of morality, deontological/utilitarian/etc, then empathy is almost certainly not required to calculate morally correct actions. But this seems to be talking about intuitive morality. It's asking: is empathy, as a cognitive faculty, necessary in order to develop an internal moral system (that is like mine)?

I'm not sure why this is an important question. If people are acting morally, do we care if it's motivated by empathy? Or put it this way: Is it possible for a psychopath to act morally? I'd say yes, of course, no matter what you mean by morality.

If someone gives me a new creature, there are things that I can do to ascertain whether it is a fish. The only question is how quickly I could do this.

Are you talking about the biologist's stipulated definition of "fish"? This is different than one's intuitive concept.

I think this is a little unfair. For example, I know exactly what the category 'fish' contains. It contains eels and it contains flounders, without question. If someone gives me a new creature, there are things that I can do to ascertain whether it is a fish. The only question is how quickly I could do this.

We pattern-match on 'has fins', 'moves via tail', etc. because we can do that fast, and because animals with those traits are likely to share other traits like 'is billaterally symetrical' (and perhaps 'disease is more likely to be communicable from similarly shaped creatures'). But that doesn't mean the hard-and-fast 'fish' category is meaningless; there is a reason dolphins aren't fish.

I actually tried the 2-4-6 puzzle on both my brothers, and they both got it right because they thought there was some trick to it and so kept pressing until they were sure (and even after ~20 questions still didn't fully endorse their answers). Maybe I have extra-non-biased brothers (not too likely), or maybe the clinical 2-4-6 test is so likely to be failed because students expect a puzzle and not a trick. That is to say, you are in a position of power over them and they trust you to give them something similar to what they've been given in the past. Also there's an opportunity cost to keep guessing in the classroom setting, both because you have less class time to learn and because if other students have already stopped you might alienate them by continuing. Point is, I've seen markedly better results when this puzzle is administered in a casual or 'real-world' setting. I intend to try it on other people (friends, co-workers), and see if the trend continues. Anyone else tried it and gotten this result?

I feel obliged to point out that Socialdemocracy is working quite well in Europe and elsewhere and we owe it, among other stuff, free universal health care and paid vacations. Those count as "hidden potentiality of the real." Which brings us to the following point: what's , a priori, the difference between "hidden potentiality of the real" and "unreal"? Because if it's "stuff that's actually been made", then I could tell you, as an engineer, of the absolutely staggering amount of bullshit patents we get to prove are bullshit everyday. You'd be amazed how many idiots are still trying to build Perpetual Motion Machines. But you've got one thing right: we do owe technology everything, the same way everyone ows their parents everything. Doesn't mean they get all the merit.

The solution here is a stopgap that just diminishes the urgency of technology to grow organ replacements, and even if short-term consequentially it leaves more people alive, it in fact worsens out long-term life expectancy by not addressing the problem (which is that people's organs get damaged or wear out).

[parody mode]

Penicillin is a stopgap that just diminishes the urgency of technology to move people onto a non-organic substrate, and even if short-term consequentially it leaves more people alive, it in fact worsens out long-term life expectancy by not addressing the problem (which is that people live in an organic substrate vulnerable to outside influence)

[/parody mode]

Have you ever heard the saying "the perfect is the enemy of the good"? By insisting that only perfect solutions are worthwhile, you are arguing against any measure that doesn't make humans immortal.

What if, instead of deciding whether the doctor murders the patient in secret when she comes to the hospital, we have to decide whether the government (perhaps armed with genetic screening results seized from a police databases and companies like 23andMe) passes a law allowing police to openly kill and confiscate organs from anyone whose organs could presumably save five or more transplant patients?

As far as I can tell, this would have no bad effects beyond the obvious one of killing the people involved - it wouldn't make people less likely to go to hospitals or anything - but it keeps most of the creepiness of the original. Which makes me think although everything you say in this post is both true and important (and I've upvoted it) it doesn't get to the heart of why most people are creeped out by the transplant example.