The modern theories of information opened to way to extraordinary new tools for communication and knowledge construction. When identified instead with the world (DNA is a complete information carrier and a program for ontogenesis, atomic particles and planets exchange information …), a new form of scientism affects knowledge and trust in science. Vague and implicit assumptions, with no precise references to the sciences of information, force strong consequences, in biology in particular. Similarly, the powerful optimization methods that make intelligible the dynamics of inert matter are expected or used to direct also human activities and replace human government by automatic governance. We are then meant to follow the formal, mechanical rule or the unique optimal path, instead of inventing new forms of sense in human interactions. Yet another fantastic tool, the newly available Big Data, is being considered to substitute scientific invention by correlations among numbers: fortunately, mathematics a priori shows that a deluge of spurious correlations may be found in any very large set of numbers. An ethics of knowledge may then be proposed in order to reconstruct the trust in science, as critical thinking at the heart of democracy.