Your family (I hope). Calling your dad a racist will provoke the reaction Urban describes. Other examples include: your job, church, club, political party. All of these groups have an orthodoxy that defines them. If you were not an adherent, you wouldn't be there. As it happens, liberalism is one of these echo chambers. Just try defending Hitler and tell me how it goes.

The echo chambers at Abbey Road were decent, if little used now.