the former is much easier to sell to the public since it tells them they have little to lose if they like the system they have.
Except that then the person opting-out doesn't "pay their fair share" but gets the supposed "benefits" because those who stay in the program, whatever it is, supposedly alleviate whatever it is "bad" that the program is supposed to solve.
Like childhood injections. By everybody else getting the shots, my kid is "protected" even though he didn't get the shots.