Critics definitely consider the personal benefit. The problem is that they don't trust that it'll actually be there, or that it's a system that actually can work as it has been designed.
For example, in the 80 years that it's been in effect, the OASDI tax rate has increased sixfold and then some. That increase was fairly steady for a period of time - and the reason it's stagnated recently is not because the tax revenue is sufficient (it isn't) but because political ramifications have prevented the tax rates from increasing. Obviously this isn't sustainable. You can say, "well, the solution is just to raise taxes" - but relying on periodic changes to tax rates is not a recipe for creating a system that can achieve a stable steady state without being subject to political meddling in the long-run.
A further problem is that Social Security hinges upon the idea that the current working population will be responsible for paying for the current retiring population. Unfortunately, the respective sizes of these populations can vary dramatically, which means that some generations will end up paying far more than others. People talk about Social Security like it's true time-shifted income (ie, savings), but it's not.
One way we've dealt with this so far is to increase the number of people who are paying into the system while remaining ineligible for collecting benefits from it, but that's also not sustainable (and it's also a really horrible way to treat people).
Once again, getting the state involved just makes things messy. Let people be responsible for their own well-being as they age. Without safety nets, people tend to be much more cautious and thoughtful when spending. Plus, people who are fit to raise smart and healthy children will also be more apt to do so, which is a must for any society!
Wealth inequality being what it is, yes, the wealthy can afford to chip in for the well-being of the rest of us. Or rather, we can afford to redistribute our wealth claims as a society in this way.
Why not? Wealth is a logical fiction we've invented, as to who has what monetary claims we enforce, and we can bend this fiction to our goals (including, as stated, the moral imperative to provide comfortable old age for all, regardless of personal means).
https://www.fool.com/retirement/2016/11/24/the-stunning-effe...
"Researchers at the CBPP used the Census Bureau's definition of poverty, which in 2015 meant $11,367 or less for an elderly individual, $14,342 or lower for an elderly couple, and $24,257 or less for the average family of four, and compared poverty rates for the elderly (ages 65 and up), adults (ages 18-64), and children (under age 18) with and without Social Security benefits.
The findings showed that Social Security benefits have kept nearly 22.1 million Americans out of poverty, with a reduction in poverty rates observed in all 50 states and Washington, D.C. As you might have rightly imagined, the bulk of those being kept out of poverty are elderly Americans, which comprise about two-thirds of all enrollees to begin with. However, children and adults younger than 65 benefited, too.
In total, 15.07 million elderly folks, 5.94 million adults, and 1.08 million children are all lifted above the poverty rate thanks to monthly Social Security payments. For all ages, Social Security reduces the estimated poverty rate in American 7 full percentage points to 13.5% from an estimated 20.5%. But the biggest effect is seen on seniors.
https://g.foolcdn.com/editorial/images/419987/ss-elderly-pov...
As you can see above, without Social Security income, just over four in 10 seniors would be living at or below the poverty rate. With Social Security income, just 8.8% of seniors are living in poverty. We'd obviously like to see that figure fall to 0%, but for such a vulnerable group of individuals who may not have other forms of income beyond Social Security, this data would imply that the program is doing its job."
What would the transition from our current state to one with significantly altered monetary claims look like? Would it be a voluntary transition, or a forceful one?
(E.g.: What is it for you to own land? It's the ability to have me forcefully expelled should I walk on it against your wishes. What is it for you to own a car? It's the ability to have me forcefully prevented from or punished for driving it myself. Etc., etc.)
To bend the wealth distribution is just to say: Ok, we as a society no longer recognize you as having $X amount of wealth, as we were doing before. We now recognize you as having $Y amount of wealth, and will carry on our claim enforcement mechanisms accordingly. We can bend the wealth distribution anyway we like… so long as we collectively decide to. (Sometimes we call this "taxation", sometimes we call it other names, but let's never lose sight of the fact that wealth, in the relevant sense, is a social construct in the first place, not a brute fact. It's numbers written down somewhere that we continually agree to.)