It's true that culture can give you a sense of legitimity that will wear off the feeling of being an imposter. But cultures always have an agenda, and they give a positive feedback only if you follow it. Unfortunaly i have yet to met a culture whose agenda is to raise happy people. So you are still an imposter, you just don't know it, and worst, you feel entitled because you respect your cultures values. And well, let's just say than on all important topic such as sex, personnal growth, feeling, suffering, happiness, etc. I never witness a culture that I could label sane. Not necessarly evil, but not a power of good either.