I do agree that's a reasonable read of "illegal" (i.e., "I'm not responsible for downstream illegal misuse"), but I think "immoral" problematically covers all manner of legal activities, from advertising alcohol to proselytizing for an unfavorable deity, depending on who you ask.

@apsillers I see from your profile that you live in the USA, which still has the Mann Act on its books. This originally "...made it a felony to engage in interstate or foreign commerce transport of 'any woman or girl for the purpose of prostitution or debauchery, or for any other immoral purpose'". It has since been amended because of ambiguity of "immoral". IMHO the licence condition is reasonable: it provides some protection in the case that one of your users offends "the morality police" in certain countries that I needn't name.

Regarding the defense against a loss due to a bug, the license has a stronger method in it: The disclaimer of all warranties and liabilities. That will keep you safe even if you cannot claim immoral or improper use of the software.

It seems a strange concern - if I buy a hammer at a retailer, I don't have to agree not to use it to damage my neighbour's car. The existing system works well enough - neither the retailer nor the manufacturer would be in trouble if I did that - only me. (For the record, I do like my neighbours, and I wouldn't actually do harm to them!)

@BartvanIngenSchenau "...the license has a stronger method in it: The disclaimer of all warranties and liabilities...". The licence means what a court says it means, not what the author thinks it means.

I don't think you can reasonably argue that a very standard form of licence disclaimer is not valid because it hasn't been adjudicated in this particular (hypothetical!) case, whilst also arguing that a very odd licence disclaimer must implicitly have validity.

@SimonCrase, what I mean is that if I use your hotel booking software to run a regular, reputable hotel and I incur a loss due to a bug, then you still have a defense: By accepting the license, I accepted that the software was provided without any warranties and that I would have no recourse to reclaim any losses. That defense relies on widely used and well-known principles in software licenses and not on having to prove that I violated a vague term like "immoral or improper use".

In the case of the Mann Act it seems "immoral" was basically clarified to mean "any kind of sexual activity for which any person can be charged with a criminal offense". In the context of software, we might interpret this to include "sexual material" as well as activity, or using software to try and reach minors with illicit intentions, stalking, and so on (seemingly on the rise nowadays), even if the use is not explicitly illegal. Going into explicit detail about such things might have made the text become too unstomachable, so perhaps "immoral" was simply the least bad word choice.

@MadHatter I'm glad you don't think that, because I never made any such claim. You are arguing against a perverse reading of my comments.

@BartvanIngenSchenau "By accepting the license, I accepted that ..." A court might agree with you, or it might not. It depends on the jurisdiction.

@SimonCrase well, you're definitely arguing that the standard disclaimer may not be valid because it hasn't been adjudicated in this case ("The licence means what a court says it means, not what the author thinks it means") and you're also arguing that the illegal-and-immoral clause protects the developer ("I have a defence: they were outside the terms of their licence"). So it seems to me that you are very much making a logically-indefensible argument, and no particularly perverse reading is required.

@Madhatter I suggest that you try to understand the difference between "some protection", which were the words I used, and "being protected". And, please, if you persist in misreading what I wrote, don't attribute the mistake to me. I agree that "no particularly perverse reading is required", but you seem to manage without being required.

@SimonCrase it would be more helpful if instead of saying what argument you are not making, you would say what argument you are. The licence currently contains two disclaimers: one of which is valid in all circumstances, and one of which is only valid in some. Why do you think the second is more protective of the developer than the first?

It seems like we're talking about different nuances of "reasonable". In the OP question, there's the statement "[the illegal-immoral-improper clause] it's not something a reasonable person could agree to" and @MadHatter seems to be talking about the last paragraph, whether it's reasonable to assume one can apply his own definitions to these things, and finally in the comments about what is a "reasonable" reading of certain ambiguous terms.

It seems to me that @SimonCrase is saying "yes, a reasonable person can agree to it, because it may offer some protection". However I still think it's not disputed that it's not an open source license. Treating it as open source would not be reasonable, but using it in some other context? Maybe it's fine and you can accept it in that circumstance, even if you're not really sure about what this immoral clause is really all about.

As I understand it, Simon advocates that s5f affords some protection over and above ss6-8 because "those only mean what a court says they do". My objection is that that weakness applies equally to s5f. If the license means what it says on its face, then the protections of ss6-8 apply in all circumstances, and cannot therefore be further extended by any other section. If it doesn't, then no other section can be held to offer any particular protection either.