Basically, people want to have their cake and eat it too. The same people who bitch the loudest about entitlements are the ones who will probably bitch the most about how meager those entitlements are when it comes their turn to receive them.

Just as a thought experiment, imagine that the tax code was structured so that taxpayers could opt out of contributing to social programs. Just check a box on your tax form and your taxes are reduced by whatever percentage would go toward funding such programs. There are just two catches: 1) if you don't contribute, you don't benefit and 2) once you opt out, you can never opt back in. Check that box and you're no longer part of the social welfare system. You'll pay less taxes, but you'll receive no benefits. You'll never be eligible for Social Security, Medicare, EBT (Food Stamps), unemployment assistance, educational assistance or any other sort of government help. If you lose your job, you starve. If you can't afford to send Junior to college, forget about a Pell Grant or guaranteed student loan. If you get sick and are unable to pay for care, you die.

Even faced with the possibility of such dire potential consequences, a large number of people would still choose to opt out. Why? Because they're greedy and are willing to take short-term gains over long-term security.

Then, as time elapsed, many of those people would discover that opting out was a big mistake. They'd discover that the government was serious about the "no contribution, no benefit" deal. The amount of self-induced suffering that would ensue would be so great that people would be rioting in the streets demanding that the opt-out provision be done away with.

Within a generation, we'd be back to mandatory participation, only people would probably bitch about it a whole lot less. For a while.