The question is whether they should trust scientists about policy decisions, not whenther they should trust scientists about science. Political/ideological decisions don't have to rely on science, this "political scientism" is a very recent thing. The entire 60s revolutions for example were primarily anti-technology, anti-corporatism and anti-established science. Part of progress is breaking up with established ideas, and that includes bad science (e.g. the neoliberal economic approaches). This applies of course mostly to social sciences, it's pretty pointless to fight the laws of physics