This is the Right Wing Kulturkampf ur-myth restated. Once upon time we were all good and well-behaved, if plagued by demons and temptations within. You know, back in the day, when lynching was a spectator sport, children were worked to death in factories and mineshafts, and employers thought nothing of hiring goons to beat and kill workers who dared strike for safer working conditions and decent pay.
Then came the Fall, and with it moral relativism, post-modernism, Freudianism, Marxism, feminism, birth control, Roe v. Wade, situation comedies that make dad into a buffoon, and black people who expect to live in our neighborhoods and send their kids to our schools...whoops, did we say that last one out loud? We meant entitlements, the nanny state, and the culture of dependence brought about by Welfare.
The temptation when things are bad now is to drop back into a mythologized history, one that never existed. As Mannion points out, this history isn't just about barbecues and social order--it has aspects we cannot in good conscience try and bring ourselves back to. Slightly more sophisticated indulgers might admit to the horrors of the past, but say they can be excised from the revival--we can bring back the community feeling of the 50s without also resurrecting the "segregated" part of said community. I applaud these people for at least recognizing that their collective past was not, in fact, idyllic, but it still misses the point: the whole schema of these time periods were intricately tied together--good and bad. This feeling of "community" that is so exalted, for example, was sustainable because it was socially permissible to exclude mistrusted minorities from the endeavor. It's easy to be friendly and neighborly when your entire neighborhood is of one race, class, religion, and mindset.
The root of this falsification is nothing too complex: It's just easier. This is liberalism's strategic (not moral) flaw. It's asks people to run an endless marathon. History is an endless struggle for moral progress (though there is no guarantee that at any given moment we are moving forward instead of backwards). There is no place on the horizon where we can rest and say "We're here. We've reached paradise." Justice being an ideal, chasing it is like chasing infinity. Not only that, but liberalism has to always pick at its own scab. We have to constantly emphasize the failings of the present, constantly remind the people that the journey continues.
This isn't a moral indictment of liberalism. The search for Eden may be fruitless, but it is still a worthwhile quest. And just because we can never get to the end doesn't mean we haven't made progress--real progress. But the gaze out into infinity can be paralyzing; is it any wonder that some wish to grasp something concrete and say "this, this was what the world should have been"?