I used to be strongly in favor of letting people opt out of SS, because I figured I could do better saving for retirement on my own and so can everybody else. I was right about the first part, but the fact is that if you let people opt out, you're going to have a whole bunch of people suddenly realize that they're too old to work anymore and they don't have any way to sustain themselves in old age.
It sucks, but we have to make allowances for lazy, short-sighted, and unlucky people, and those allowances might come at the expense of people who are more responsible. (This could be the unofficial motto of Gen X).