This is not a helpful comment. Why do you not find it interesting that religious extremism is better at motivating people to do rational goal-achievement analysis than a modern scientific culture?

Regardless of the factual basis of either claim, they're each focusing on the sexual practices their readers are most likely to condemn their enemy for engaging in. It's Dark Arts 101.

This is a bit ambiguous. You could mean 'They're focusing on sexual practices their readers dislike, without concern for the factual basis of their accusation. Therefore it's Dark Arts.' Or you could mean 'They're focusing on these sexual practices because their readers dislike them. Therefore, regardless of the factual basis of their accusation, it's Dark Arts.'

If the former, then I'd like some evidence that news organizations are fabricating a rape scare (or a promiscuity scare). If the latter, then I disagree; it's not Dark Arts to criticize a group for unpopular sexual practices, if the practice in question is genuinely harmful. This is especially clear if the harmfulness is a big part of the reason it's unpopular.

You seem to be using 'rational' here to just mean 'good'. So your point is 'It's disturbing that people sometimes do good things for bad reasons'.

PhilGoetz's post is pretty thin but I'm not sure he's guilty of that specific confusion. He may have made edits since your comment, but at the moment it says

What I find so disturbing about this is that humans need to have a religious justification to act this rationally. No "reasonable" society would encourage women to use sex to seriously motivate what they think needs to be done.

which reads to me not as a use of "rational" to just mean "good", but a use of "rational" to describe (supposedly) instrumentally rational behaviour. The point PhilGoetz is getting at (if I read him correctly) is less "It's disturbing that people sometimes do good things for bad reasons" and more "It's disturbing that people need an epistemically irrational basis for being so instrumentally rational".

Granted, PhilGoetz has shot himself in the foot here by (1) expressing that in a way that's simultaneously provocative and easy to misinterpret; (2) implying that travelling thousands of kilometres to a war zone to screw soldiers is an efficient (and hence instrumentally rational) way to further the cause of fundamentalist Islam, which I doubt; (3) implying that a reasonable society would "encourage women to use sex to seriously motivate what they think needs to be done", without acknowledging likely problems with such a strategy; and (4) using an example that could well be BS, since the only source here is Fox News quoting a Tunisian minister who's vague & imprecise:

"They have sexual relations with 20, 30, 100" militants, the minister told members of the National Constituent Assembly [...] He did not elaborate on how many Tunisian women had returned to the country pregnant with the children of jihadist fighters. [...] The minister also did not say how many Tunisian women were thought to have gone to Syria for such a purpose, although media reports have said hundreds have done so.

I'm perplexed that you imagine I think that having sex with jihadists is good. No; I mean rational: Their society wants to encourage men to become jihadists, so they encourage women to provide sex to jihadists. (Supposing that this even happens, which I doubt--I can't find any references to it older than Dec. 2012, and the main sources are Iran and Fox News.) This is strictly rational for the religious leaders who allegedly support it, as there is zero cost to them.