I used to rant about Boomers and Social Security, complaining that all their money was parked on the shores of Vietnam. It's kind of true afterall. But I changed my mind for a few different reasons. 1) as mentioned above the drumbeat of empirical data that most people don't save enough. Second though was the realization though that most of the cost increases were driven by life span increases and demographic transition. Life span increases may continue incrementally, but the demographic transition is nearing maturity (aka the percentage of the population in different age categories is closer to stabilizing). Three no one complains when private companies fail to meet 10, 15 or 30 year projections. With my school budgeting experience I came to viscerally appreciate the importance of modest year to year corrections. Without that level of adjusting any 30 year projection for any company or government is going to end up either controlling the world because they have made so much money or be bankrupt many times over.
Also remember our SSI is 13%, 6.5 from you and 6.5 from your employer. Very small changes in the program now would have a very large impact on how long there continues to be a SSI 'surplus'

The surplus is actually one of the last things I realized is problematic. What would happen to the stock market if a mythical investor let's call him Warren Gates, suddenly bought 3 trillion dollars in stocks(AKA the value in the trust fund)? Of course it would over inflate prices on tons of stocks, Buffet has made a lot of comments during the last Bull market for not having enough places to park merely Billions in cash because the value isn't there. So there is reason to be concerned about over supplying the stock market with capital, when there are plenty of very useful investments like roads, bridges and public health that generate huge economic benefits.