The only type of person I can think of that truly does this is the hermit, for even monks or cloistered religious (or any other ascetic that lives in community with others) retain the semblance of civilized life, if only the most noble parts. Prophets also do this, to the extent that they do not care whether they live or die, and instead devote their life to, as it were, ‘waking’ others to the urgency of reality as they perceive it to be. But, by necessity, they must dwell among humankind, and go forth among their civilized brothers and sisters, delivering their message by whatever mode of expression is most natural to them. So that they never really abandon civilization, though they are concerned with its spiritual condition above all else.