However, I'd add an important corollary, and one that is perhaps a bit less cynical :). Even if it's mostly true that you can only feel fulfilled when your actions and opinions are approved by your peers, you still get to chose who your peers are, and whose opinion you value. That's true today more than ever, with the world's interconnectedness and the huge diversity of on- and offline communities.
Near the end of the article, Mark Twain says "Men think they think upon great political questions, and they do; but they think with their party, not independently." If you take the time to choose the parties/communities you align yourself with carefully, you can live a very principled and self-determined life even accepting the inevitability of some degree of group conformity.