Innovation is good; financial innovation is bad. It gave us the global financial crisis, after all, along with multibillion-dollar bailouts for entities such as AIG Financial Products, which almost nobody had heard of before they suddenly turned out to pose a mortal threat to the entire economy.

That said, there are two financial innovations that are generally considered to have been clearly positive for society. One is the ATM, for reasons which should be self-explanatory. The other is passive investing. Rather than pay a financial professional large amounts of money to pick securities for them, passive investors simply pay a very modest fee to buy a broad, predetermined, diversified basket of stocks. It’s easier, it’s much cheaper, and it almost always outperforms the active investors over the long term.

Felix Salmon (@felixsalmon) is an Ideas contributor for WIRED. He hosts the Slate Money podcast and the Cause & Effect blog. Previously he was a finance blogger at Reuters and at Condé Nast Portfolio. His WIRED cover story on the Gaussian copula function was later turned into a tattoo.

The passive-investing revolution is, wonderfully, well upon us: Every year, billions of dollars flow out of active managers and into index funds or ETFs. The biggest passive managers, Vanguard and Blackrock, are now the undisputed giants of the asset-management space, each controlling trillions of dollars.

Neither of them, however, has a reputation for being particularly consumer-friendly. It’s almost impossible to open an account directly at Blackrock; to a first approximation, nobody does so. And Vanguard has an atrociously-designed website where the login process alone makes you want to run screaming.

Enter the “roboadvisers,” so-called because they take the work done by old-fashioned human financial advisers and use algorithms to perform it instead. Led by Wealthfront and Betterment, these firms are young, mobile-first, and backed by millions of venture capital dollars. They know where the puck is headed (millennials investing passively), they’re up to speed on all the latest behavioral economics, and they can use modern technology to make it easier than ever to just hand your money over, answer a few questions about your risk appetite, and sit back, safe in the knowledge that no one’s going to be gambling your money away.

For the past few years, that has put both Wealthfront and Betterment in a happy position where they can credibly claim to be doing well by doing good. Both of them, until now, have been perfectly aligned with the passive-investment revolution. The more that either of them grows, the better invested America will be, even as both of them have the potential to make serious money. Extrapolating out a few years, if either company ever got to just 1% of the $33 trillion of investable assets in America, their modest annual fee (one quarter of 1% of assets invested) would amount to $825 million per year. Those sums have caused venture capitalists to throw almost $500 million at the two companies combined ($205 million for Wealthfront, and $275 million for Betterment).

Recently, however, the industry has started to encounter some problems. Neither Wealthfront nor Betterment, it turns out, has seen the kind of exponential growth that VCs tend to look for; both of them have seen their growth rates level off or even fall since mid-2015. Millennials might control a majority of investable assets in 2030, but there’s no way of speeding up time between now and then.

What’s more, it can be hard to sell these products. Financial sophisticates who understand the advantages of passive investing have a tendency to just buy ETFs or index funds directly, rather than getting a middleman to do it, while less sophisticated investors often struggle to understand just what it is that makes these companies better than their competitors.

The robo industry, looking for extra sources of revenue, is therefore beginning to move away from the passive-investing ideals that excited so many of its early adopters. And Wealthfront in particular is doing so in a very troubling manner.

What we’re seeing is an inflection point like we’ve seen at other digital businesses in the past: Stay true to your ideals, or follow the money? Airbnb, for instance, has at this point moved far away from its original vision of fostering personal connections through sharing homes and spare rooms. Instead, it is trying to become as institutional and friendly as possible to business travelers and others who have no desire for human interaction at all. Craigslist, meanwhile, has stuck to its guns, leaving billions of dollars on the table while doing so.