This One Goes to Eleven (Robert Wright & Mickey Kaus)

[DWAnderson]

Here's the problem with heavy means testing entitlements so that they only prevent poverty: it imposes stifling effective marginal tax rates on the working poor, the faster you phase out the entitlement benefits. This is doubly true for means testing social security (based on income): it would discourage the elderly from working and it would discourage them from saving.

This is why social security isn't really a cash cow at all because when push some to shove, even our elected officials are not usually dumb enough to impose 70%+ effective marginal rates on the working poor.