Could be that their parents believed it because that is how SS was sold to the public by the Feds. And is still being sold. Very few people care, or know, about these court decisions.
If SS/Medicare deductions are added to Fed withholding deductions people might actually go into sticker shock over the amount of current taxation.
I predict the same thing will eventually happen with OCare.
The lies have been sold to the public so long and so well that it is very hard to break through that hardened shell of practiced ignorance with the truth.
My mother grew up during the FDR years and I had to tell her any number of time that there is no SS Trust Fund and there never was before I think she finally believed me. She also started listening to Mark Levin on the radio because it preceded her favorite show.
It is difficult to convince most people that people in authority are at least misleading them and most likely boldly lying about things that truly matter to their future wellbeing.
People by education and natural inclination will accept the word of their leaders unless or until personal experiences teach them otherwise. Once the barrier of trust is broken the truth becomes obvious.
There are those of course who are ideologs and see truth through that ideology. To them the truth is secondary, superfluous or a tool to the ends they seek.
The biggest impediment to getting people to see the truth about SS is that in this case to most people The Truth Will Set You Free is not they way they feel. People do not want to believe that their government can at any time pull SS out from under them. This is a truth that for many puts them at risk of poverty in their old age. For many people SS is a major part of their retirement plans. Telling these people that SS most likely will be broke before they retire is not a truth they want to hear and definitely not one they want to believe.
I have heard politicians on the Left and on the Right spout the pleasant to hear lie that SS is solvent and will be around for a long time to come. Most in government do not want the general population to know that the 15% of their income that has been deducted from their hard won earnings for many years has gone down the rabbit hole of wasted government spending and that they will never see it again. Such truth makes for angry voters.