When middle class wages go up, small businesses open, they employ more people, creating more middle class people, and the cycle continues ad infinitum. The middle class pays the bulk of the taxes since they lack the finances to avoid them, and additionally is responsible for creating the bulk of the jobs in small business. The middle class also leads consumption. See the previous point for why this is important.

If the middle class fails everything below them fails. The only people that win in all scenarios are the ultra wealthy. If the middle class cannot retire, effectively no one can retire. Since their suffering is magnified in the lower economic strata.