For the record, despite my ambivalence toward supermajority requirements for legislation, I have no problem with this liberal push to require a two-thirds majority for cuts to Social Security. Insofar that we have a long-term debt problem, Social Security has little to do with it, and proposed cuts have more to do with furthering the conservative agenda than they do with fixing our finances. Liberals should use every tool they have available to oppose this nakedly ideological tool.
Relatedly, it's worth noting how the entire conversation over Social Security takes place under an anti-tax paradigm. The most praiseworthy "reformers" -- Republicans, "centrists," etc. -- are those that propose cuts to a program that sends most of its benefits to middle and working-class seniors. By contrast, because it involves higher taxes on wealthier people, it's not "realistic" or "serious" to suggest a broader tax base for the program, despite its simplicity and effectiveness. As Ezra Klein points out, you could "wipe out virtually all of Social Security's shortfall" by lifting the payroll-tax cap so that all got taxed, rather than just the first $107,000.
I don't begrudge conservatives for their opposition to Social Security, but I wish the media would acknowledge that this conversation isn't actually about deficit reduction: It's about the legitimacy of the welfare state and whether the non-rich deserve protection from the vicissitudes of life.