CellBioGuy isn't (so far as I can tell) trying to force employers to pay women the same as they pay men (that would count as "demanding" and might be unethical); he's merely saying that he thinks they should pay women the same as they pay men. Do you really think there is an ethical problem with saying that? (Er, of course you might disagree, but it looks as if you're saying more than that: that CellBioGuy is doing something unethical merely by expressing that opinion.)
He is of course free to say anything he wants to and I have no ethical opinion on him saying what he believes, but that's not what is under discussion.
If somehow a society gets into a state where people with blond hair are paid 20% less than everyone else for equivalent work, then that 20%-lower figure is the market price, and offering more than that would be (in your terms) "a gift", and so -- if your argument is right -- it would be wrong (not merely incorrect, but unethical) to say that employers really shouldn't be paying blond-haired people 20% less than everyone else.
If they paid 100% to the blonds, then they eliminate any benefit to them from hiring blondes in particular, and reduce the rate at which this inequity is wiped out. Anyone who establishes a norm of full pay has harmed their cause. This is as predictable as a refusal to buy from sweat shops harms the sweat shop employees and the economic development of that impoverished country. The private good here helps create the public good of an equitable country. If one cares about things like consequences, then yes, it would be unethical to overpay the blondes. You should pay them slightly above market-wage, and you morally owe them nothing further as you have helped to erase the inequity.
Of course, one could give them more money. But this is not ethically superior to other forms of charity like donating to Against Malaria Foundation, and is much worse than many forms of charity: you're giving money to someone stable, able-bodied, not just employable but actually with a job, and (in the relevant countries which have the luxury of feminists searching out discrimination) who lives in a First World country - the sort of people who least need your charity.
If they paid 100% to the blonds, then they eliminate any benefit to them from hiring blondes in particular,
Not necessarily (assuming by “they” you mean an individual employer rather than the market as a whole) -- in that scenario, the most qualified blond willing to work for 100 will be more qualified that the most qualified brunette willing to work for 100.
LW readers have unusual views on many subjects. Efficient Market Hypothesis notwithstanding, many of these are probably alien to most people in finance. So it's plausible they might have implications that are not yet fully integrated into current asset prices. And if you rightfully believe something that most people do not believe, you should be able to make money off that.
Here's an example for a different group. Feminists believe that women are paid less than men for no good economic reason. If this is the case, feminists should invest in companies that hire many women, and short those which hire few women, to take advantage of the cheaper labour costs. And I can think of examples for groups like Socialists, Neoreactionaries, etc. - cases where their positive beliefs have strong implications for economic predictions. But I struggle to think of such ones for LessWrong, which is why I am asking you. Can you think of any unusual LW-type beliefs that have strong economic implications (say over the next 1-3 years)?
Wei Dai has previously commented on a similar phenomena, but I'm interested in a wider class of phenomena.