Synthetic biologists are extremely concerned with responsible research and innovation. This paper critically assesses their culture of responsibility. Their notion of responsibility has been so far focused on the identification of risks, and in their prudential attitude synthetic biologists consider that the major risks can be prevented with technological solutions. Therefore they are globally opposed to public interference or political regulations and tend to self-regulate by bringing a few social scientists or ethicists on board. This article emphasizes that ethics lies (...) beyond prudence and requires a cultural evaluation of the modes of existence of the various microorganisms designed by synthetic biologists, independently of their potential applications. (shrink)