“Culture is not your friend. Culture is for other people’s convenience and the convenience of various institutions, churches, companies, tax collection schemes, what have you. Culture insults you. It uses and abuses you. None of us are treated well by culture...We have to create culture, don’t watch TV, don’t read magazines, don’t even listen to NPR. Create your own roadshow.”
McKenna is saying that if you don't consciously build your own meaningful culture in your life, it will be determined for you by dominant personalities, media, propaganda, peers, advertising, and all kinds of other capricious influences who have no business being in your head and determining your preferences and actions.
Life is short, and progress towards virtue is often time consuming and hard won. You should be very selective about what you devote your precious and limited time to. If you want to be happier, cut out expressions of culture that sabotage your happiness and personal growth, and deliberately create your own personal culture of beauty and meaning based on your values, rather than on other peoples'.