That isn't the worst case. The Windows using victim* could install something accidentally by careless clicking (the "Yes,Yes, Yes" Windows installer process).
I recognise you are treading a fine line between defending a company you feel a duty to and practices and business model that you probably wouldn't select for Y-Combinator on the publicly visible business model. I hope they pivot to a less controversial model and leave you in a more comfortable place.
* You are right that the users are the advertisers but that must make the person running the installer the victim or at best the product.