I think you prove the point you're denying. You say you don't need fancy algos, but companies are wasting advertising on your gf by using basic indicators (age, sex) when in the Target case the advertising was, well, targeted.

If advertisers know what will get you to push the buy button then they can use that against you. Advertising pregnancy pants to those who aren't pregnant will almost always fail, and from the advertisers perspective it wastes an opportunity to push a product that you might buy.