A time is marked not so much by ideas that are argued about as by ideas that are taken for granted. The character of an era hangs upon what needs no defense. Power runs with ideas that only the crazy would draw into doubt. The "taken for granted" is the test of sanity; "what everyone knows" is the line between us and them.
This means that sometimes a society gets stuck. Sometimes these unquestioned ideas interfere, as the cost of questioning becomes too great. In these times, the hardest task for social or political activists is to find a way to get people to wonder again about what we all believe is true. The challenge is to sow doubt.