I mean “zombie” in the Paul Krugman sense of “an idea that should keel over and die forever, but keeps hanging around.”
One strong candidae I know is the notion that government debt is just like family-household debt, but at least that has a bogus grounding in “common sense.”
No the Grande Zombie has to be “Social Security is DOOMED or at least must be made means-tested!!” The means-testing argument — grant social security more to those who need it most — would simply turn it into another “entitlement,” which are much easier to cut and eventually eliminate than benefits guaranteed to everyone.
The ultimate is the “SS is going broke!” cry of alarm. “Well, that can be fixed by just raising the top income taxed …” “LALALA can’t hear you — SS is going broke!!” From day one the argument sounded like the yelps of those who never have and never will need SS checks and don’t want to drop a penny to support yours. Took me far too long to accept there were those that callous toward their fellow citizens.