Targeted advertising needs to end
Targeted advertising simply needs to be outlawed, full stop. It is not at all comparable with advertising fishing tackle in a fishing magazine or wedding dresses in a bridal magazine, where there is some expectation of a theme. It's literally messing with people's heads; subverting the entire concept of "universality of experience" in a way, and to an extent, which is tantamount to psychological warfare.
It's no coincidence that the UK has become more openly racist since the Brexit referendum, because the cheating Leave campaign worked by emboldening racists. They carefully targeted a series of advertisements only at people they already suspected of harbouring some racist sentiment, in order to create a false impression that the racism in the adverts was socially acceptable. And their legacy is a whole bunch of people wandering around, believing there is nothing wrong with being openly, boldly racist to people.
Racists do not exist in a vacuum. Racist Uncle Joe knows not everybody shares (indeed, has met people who do not share) his racist views; and he knows, on some level, people find them reprehensible. If Racist Uncle Joe were to see an openly racist advertisement in a newspaper, on TV or on a hoarding in a public place, somebody he knows -- most probably even his own niece Fiona, whom he sees in real life from time to time -- would be sure at least to complain about it. And that's how he knows it's racist: because other people who have seen the same advertisement are saying it's racist.
And when Racist Uncle Joe knows Fiona is visiting the same pages as he is, but she never says anything about the terrible racism in the advertisements on the pages, then he reasons the advertisements cannot be racist enough for her to speak up.
It never occurs to him that on the Internet, it's possible for everybody to be shown different advertisements alongside the same content. Why would it? If two people look at a billboard, they see the same advertisement. If two people are watching the same TV programme from the same transmitter, they see the same advertisements in the breaks. If two people are reading the same newspaper, they see the same advertisements. It's how advertisements have always worked, since time immemorial; and it's almost unreasonable to expect .
The only way to ensure this will never happen again is to outlaw even the possibility for individual targeting of advertisements; which means stopping the collection of data which allows the targeting, requiring advertisers to deliver the same content to all clients without discrimination, and requiring it to be made easier for Internet users to block advertisements altogether. Let the wailing and gnashing of teeth commence.