This sounds good in theory, but it's exceedingly difficult in practice. Google uses a robust mix of human and machine analysis to trawl the web for ads and websites that violate its policies, but those who are interested in breaking the rules are constantly adapting to evade detection. The even bigger challenge, and one that underscores the need for involvement from lawmakers and regulators, is that Google’s policies are based on state laws, which means Google responds to the same advertisements differently in various areas of the country.

It also means Google relies heavily on leadership from officials at the local level, for better and for worse.

In Vermont, for example, there are strict rules about lending, including an outright ban on payday loans. The attorney general there has made it a priority to crack down on illegal lenders. State officials have also identified lenders and payment processors who violated the law, and shared that information with search engines so they could strip illegal advertisements from the web.

But because laws differ state by state, Google might only disallow advertising from those businesses in the state of Vermont—as long as the ads still complied with Google policies. Which means the ads delivered to a web user in Vermont, would be different than what a person searching the same terms in another state might see. (This is on top of the fact that Google’s algorithm already serves up distinct results to individuals—even people in the same room googling the same thing—based on past browsing history, location, and other data.) There’s evidence, too, that this layer of protection doesn’t even work in the states with the toughest consumer-protection laws.

Consider this finding, from an October report by the tech-policy consulting firm Upturn:

To test how payday lead generators were using major ad platforms to advertise, we ran a series search queries on Google and Bing (including, for example, “payday loan,” “need a loan fast,” and “need money to pay rent”) from internet protocol (IP) addresses originating in states with strong payday lending laws (including Pennsylvania, New York, and Vermont). In each jurisdiction, we saw many payday loan ads commissioned by lead generators.

And so, an already complicated problem becomes even more convoluted. That hasn’t stopped consumer advocates from seeking solutions. Last week, the Federal Trade Commission held a workshop about issues related to online lead-generation. Many of those involved agree that regulators, lawmakers, and those who are buying and selling data must lead the way in protecting consumers.

In other words, it isn’t only up to Google. That’s in part because search engines can establish robust policies against bad advertising without having—and, arguably, without being reasonably expected to have—enforcement mechanisms. This doesn’t mean Google isn’t responsible for the predatory ads it hosts. It is. But also: Google can’t erase them from the web by itself.