Like hundreds of thousands across the U.S. and around the world, I marched for science on Saturday. And like most who attended these events, I marched because the Trump administration both denigrates critical research on issues like climate change and has called for massive cuts in research funding. Those cuts could cripple research into climate change, weather forecasting, opioid addiction, the Zika epidemic and more.

We must support science against these attacks, but we must do so with our eyes open. At the San Francisco march I attended and in reports from the main march in Washington, D.C. and others around the globe, I heard a few things that made me uneasy.

“Science brings out the best in us,” said Bill Nye (“the Science Guy”) in Washington. In San Francisco, former “Mythbusters” co-host Adam Savage said, “Science is the rigorous elimination of bias.”

Both statements express an ideal that in reality researchers sometimes fall short of achieving. Science indeed tries to bring out our best, and it strives to rigorously eliminate bias. Ideally, the scientific method works to ensure those results. But scientists are human and all humans, whatever their background or academic degrees, have biases that color their actions, often unconsciously. Scientists can be influenced by the society in which they live, the attitudes of the people around them, and the sources of their funding – even when they try their hardest not to be, as most do.

At times that’s caused people and ideas seen as being at the margins of society to be dismissed or denigrated by mainstream scientific thought. A few years ago on this blog I wrote about how that played out in the area of immigration. As documented in Peter Schrag’s excellent book, “Not Fit for Our Society,” supposedly “objective” intelligence tests in the early 20th century produced “scientific” results that mirrored the prejudices of U.S. society, with light-skinned northern Europeans shown to be most intelligent, eastern and southern Europeans trailing and African Americans at the very bottom. One study labeled 82 percent of Russian immigrants (for the record, that would include my grandparents on my father’s side) as “morons,” with Hungarians, Italians and Jews also ranking high on the moron scale. At the time, Princeton University researcher Carl C. Brigham wrote confidently, “The intellectual superiority of our Nordic group over the Alpine, Mediterranean and Negro groups has been demonstrated.”

It hadn’t, of course. In hindsight, the cultural biases of the tests used back then seem laughably obvious.

One can look at other issues – particularly those related to human personality and behavior, which seem to be hardest for anyone to be objective about – and find similar occurrences. In its first Diagnostic and Statistical Manual of Mental Disorders in 1952, the American Psychiatric Association labeled homosexuality as a “sociopathic personality disturbance” – a view that was not at all controversial at the time. Indeed, for years only a relatively few brave mental health professionals dared argue that gays and lesbians (hardly anyone even talked about bisexual or transgender folks back then) could be as well-adjusted as anyone else. It wasn’t till 1973 that the APA, amid some controversy, decided that LGBTQ people were not by definition “mentally ill.”

None of this should be taken to denigrate science or the good it does for us. It means that we must recognize that, as one of the organizers of the Silicon Valley Science March put it, science is “a process, a toolkit, not a product.” Science seeks to look at facts and test them rigorously to sort out what is true and what is not. It’s certainly a better approach than what we too often see in politics: Starting from a belief system, then looking for facts that back up those beliefs and ignoring those that don’t. To maintain this little rock we live on as a habitable planet in a vast universe that’s mostly inhospitable to life, we need to support and fund science and listen to its results.

But as immigrants, people of color, LGBTQ individuals and others have learned the hard way, scientists can never be 100 percent immune from the biases that infect society. For that reason, we should never be afraid to ask hard questions, even of experts.

Bruce is Greenlining’s Media Relations Director. Follow Bruce Mirken on Twitter.