If you pay per view, it's entirely rational to target towards the demographic that produces the most spend for your ad budget.
Why would you waste money advertising, e.g., mascara or sanitary pads to men? Sure, there's probably some infinitesimal fraction of men who would be interested, but targeting them profitably is not a trivial exercise.
"User is a woman" would, in this hypothetical example, be one factor in your larger weighting algorithm. A weighting factor that is, might I add, quite easy to implement compared to detecting male performing arts majors with a specialty in costume design.
Because you don't know in advance. It's entirely why advertisers offer so many different bits of information on you, to optimise this.
> I would think you'd be better of targetting people who bought some sort of eye makeup if you wanted to sell mascara, and target people who bought pads or tampons if you were selling pads.
And people do this, if they have this information. Of course, there's also the side that you don't want to advertise to someone you strongly expect to buy, because it's the conversions from no-sale to sale you care about.
In that case I suppose it's not very ethically questionable for things that are very clearly 100% (within a minuscule margin of error) men's only (prostate health, etc.) or women's only (sanitary pads).
I guess the real quandary is for stuff that's male-dominated like hard, dangerous physical labor (coal mining etc.), but not 100% men. If a recruiter can statistically prove that the most efficient use of their advertising dollars to hire for a coal mining job is by targeting only men, 1) is it sexist and/or unethical, and 2) should it be legal?
I put this at the same level as only hiring women to teach elementary school. Yes, it is sexist and uneducated. No, it shouldn't be legal.
What if you are trying to get more female engineers at your company, and want to target women?
I guess my point is an targeted ad isn't evidence of intent to discriminate, and in fact can be a key component of pro-diversity actions.
For example, buying different scented shower gel based on the sex of the recipient.