Silicon Valley tech workers are worried that Palantir Technologies, a company co-founded by Donald Trump adviser Peter Thiel, could end up helping the president-elect crack down on immigrants based on their race, religion or national origin. They should also recognize the role that they — and the companies they work for — have played in making such a scenario possible.

Last week, the workers staged a protest outside Palantir's headquarters in Palo Alto. Their demand: that the company, which sells data-mining technology to the government and other customers, prevent the federal government from using the contracted software to create a Muslim database or facilitate mass deportations. Their concerns are focused on two systems: Falcon and the Analytical Framework for Intelligence, both of which the Department of Homeland Security uses to profile individuals — including such information as social and family relationships, travel histories and addresses.

Yet Palantir's analysis tools are not terribly different from what these folks work to create every day. Technology companies already build databases that document people's ethnicity, religion and other personal information that allows them to target ads. Major networks such as Google and Facebook can infer detailed demographic information by tracking users all over the internet with cookies and device identifiers, and form partnerships with data brokers that provide the personal information needed to connect that online activity to specific individuals. One company engaged in "identity resolution," LiveRamp, says it can recognize 98 percent of U.S. adults based on online identifiers.