You make a rather well reasoned argument, but it is one with which I don't agree. First, there's the falacy that investing in the market requires some form of lucky timing if one is to come out with a secure retirement. If someone has been investing in the market for the last 30 years (since 1978) then your annualized returns have been 10%. So, if you invested $1000 in 1978 and then continued to sink $1000 per year then you'd have somewhere around $140k ($110k return on $31k of total investment). Funds are down around 10% this year (which has been about as bad a year as one could expect), so that $140k would be $124k if one was to retire this year. Even in the worst stock economic environment since the Great Depression, losses haven't exactly offset gains (nor come close to doing so).
One should also remember that you retire not with your entire portfolio, but with the portion needed for a certain time period (one month, or one year). Even in a modest and very safe investment vehicle meant mostly to maintain portfolio value in retirement, one can expect 2-3% growth, which would eventually offset these short-term "losses" (which are only real losses if you just got in the market this year).
You claim that Social Security will be there, and if it's not then there are much bigger problems in the rest of the economy. I've heard the argument before -- but the question isn't whether Social Security will be there, but in what form? Will I have to be 75 to collect? How much lower will my benefit be than people who are collecting today? You're also ignoring the oportunity cost of my 10% annualized return, which I've already shown to have been secure in the long-run. Basically, your argument is that some guaranteed return, no matter how insignificant an amount, nor how much it costs me, nor whether or not I can even hope to live to collect it is better than even a minor risk of losing everything. In fact, there is almost no mathematical potential for losing everything (or even very much if total returns over time are considered) from a well diversified portfolio -- basically you're just being paranoid and using your paranoia to justify ripping people off and ensuring that they retire poorer than they have to.