I think that having a code of conduct in an open source project is extremely important as it outlines a set of standards that users are expected to abide by. It also creates some sense of accountability to enforce these standards for all contributors. I think the existence of a code of conduct makes projects more open and approachable. I would be hesitant to contribute to a project that lacked a code of conduct. While enforcement of the code of conduct is difficult, I do feel that it is most likely achievable in a lot of cases, especially if the project is large enough to have a group of people investigate and respond to violations of the code.