Scientists are worried about the Trump administration: His pick for the Environmental Protection Agency doesn't seem interested in protecting the environment, his energy secretary lacks the publication record of his highly academic predecessors and the president himself once tweeted that global warming is a Chinese hoax. In light of such issues, they're planning a march to advocate the use of scientific evidence in political decision-making.
Was there ever an alternative to evidence? Most policymakers already believe that their decisions are firmly rooted in science. The best science. Problem is, it's often hard to distinguish between fact-based scientific evidence and marketing material. It's not even clear that the Science March organizers have a very good understanding of the issue. One of their tweets (since deleted) read: "colonization, racism, immigration, native rights, sexism, ableism, queer-, trans-, intersex-phobia, & econ justice are scientific issues — March for Science (@ScienceMarchDC) Jan. 29, 2017"
Along with a march, maybe we need better education on the difference between science and politicized pseudoscience.