Isolated libertarians

A few weeks ago, a thought experiment by Bryan Caplan attracted a lot of attention from assorted bloggers.

Suppose there are ten people on a desert island. One, named Able Abel, is extremely able. With a hard day's work, Able can produce enough to feed all ten people on the island. Eight islanders are marginally able. With a hard day's work, each can produce enough to feed one person. The last person, Hapless Harry, is extremely unable. Harry can't produce any food at all.
Questions:
1. Do the bottom nine have a right to tax Abel's surplus to support Harry?
2. Suppose Abel only produces enough food to support himself, and relaxes the rest of the day. Do the bottom nine have a right to force Abel to work more to support Harry?
3. Do the bottom nine have a right to tax Abel's surplus to raise everyone's standard of living above subsistence?
4. Suppose Abel only produces enough food to support himself, and relaxes the rest of the day. Do the bottom nine have a right to force Abel to work more to raise everyone's standard of living above subsistence?

The problem with the gedankenexperiment is that these are the wrong questions.  The right question is "what should the islanders do?"  And the answer is: they should sit down and figure out what it is that makes Abel so productive.  Caplan doesn't say what the islanders are doing to produce food, but since he speaks of a day's work on an island, let's suppose that they're fishing.  So has Abel simply obtained access to the best fishing grounds?  If so, reallocate them more fairly.  Has he devised some technique for making better fish-hooks or nets?  Then let him teach it to the others.  Does he have some innate talent at casting a line which can't be taught?  Then the islanders should fish together, Abel casting the lines and passing the fishing rods to the others to manage.

Yes, I know, Caplan doesn't concern himself with the details because he's making an analogy.  And so am I.

Oh, and let's not forget about Harry.  If the nine other islanders, with their new co-operative fishing techniques can produce enough food to feed ten, and if Harry is too infirm to assist them, then yes they should support him anyway.  Because not to do so would be inhuman.

Caplan's own analysis of the questions includes this remark, which he seems to think obvious:

Unjust treatment of the able may not be the greatest moral issue of our time...But unjust treatment of the able is a serious moral issue.

I am sympathetic to the libertarian argument that governments tend to interfere in things they'd do better to leave alone. But I find (right) libertarian thought otherwise highly uncongenial, and this observation of Caplan's may explain why. Because I simply can't see that there is any moral reason to reward ability in itself. There are moral reasons to reward work, and economic reasons to reward productivity (without attempting to discover what combination of ability and application may have given rise to it). But there is nothing in morality that tells us to reward accidents of birth or upbringing.