For example, things like television attribution providers which listen on your smartphone to try to watermark advertisements and see whether you bought something that was advertised on the RV or radio are pretty creepy. And I have heard too many anecdotes of Facebook ads showing up after conversations not to suspect Facebook is doing the same with conversations (though I can't prove it and can't be sure). The level of intrusiveness there is very high and the creepiness factor is similarly troubling.
But now let's look at something very different. Suppose you look at providers that simply do analytics on something like purchases and only share the data with the client. To my mind there isn't so much wrong with this. And you could have third party referees that can then referee disputes on whether a given click lead to a purchase or not, allowing better payment models. Those are not so problematic.
Everything I have seen in the advertising industry (print and online, etc) is that it is rife with all kinds of problems. And yet the industry exists because advertising is an important part of reaching an audience business-wise and so people put up with all the crap. So I am not sure that ad-tech needs to die. We need a better ad-tech industry. One without the creepy parts.
To this end, I think we need more things like GDPR, not less.