What prevents any of the following solutions from providing assurance to advertising clients, without also destroying the Internet and general purpose computing:
1. Building trust with advertising clients be treating them with respect, honesty and transparency. If your clients don't trust your advertising network and were demanding assurances in the form of WEI and similar proposals, surely it's obvious there are bigger problems. The advertising client would likely have dropped the advertising network long ago but can't due to monopolies existing.
2. Advertising networks undergo independent audits (results available to clients) and become more transparent to clients in how their advertising spend is being used.
3. Advertising clients survey users at checkout to ask whether they found the product/service from an advert, or whether they recall seeing an advertising campaign and where they remember seeing it.
4. Advertising clients host advertisements at ads.company.example (in a few highly restricted formats) so they can keep track of impressions themselves.
5. (still a bad idea, based on user surveys, but one which Google et al should have considered for minimisation of data collection and privacy impact) Browsers collect advertising metrics during use and when a user makes a transaction at an online store, the online store asks the user (via the browser) for permission to obtain those saved advertising metrics to provide only to the online store. Users can review the entirety of information sent to the online store before it is sent. Advertising networks don't have a need to access browsing history for everyone on the Internet in real time.
6. Online stores and similar continue to rotate their marketing spend through various advertising networks and marketing campaigns, checking their own metrics to see if advertising campaigns have been having an impact. Campaigns could include marketing using the Internet but outside the reach of Google et al such as use of campaign-specific coupons and products marketed through product review websites, referral schemes, influencers, etc.
2. Great, they should do that, but good luck doing that when the data you need to audit is on a bajillion client machines.
3. People do that already
4. This became a thing a while back as a way to defeat third-party tracking blockers in browsers
5. This is literally the attribution system you're arguing against
6. They do that already. But good luck finding an ad marketplace that Google and Facebook don't have their fingers already in.
Also...
> What prevents any of the following solutions from providing assurance to advertising clients, without also destroying the Internet and general purpose computing
I was replying to a comment asking why Mozilla supports Interoperable Private Attribution (IPA). None of what I said should be taken as support for Web Integrity, which is cancer.