First, i want to say emphatically that i am against any plan to privatize Social Security. I don't want anything i might say to be construed otherwise. Social Security was never designed to be a complete pension. It was designed to provide a lifetime stream of income so that the elderly would not end up destitute with no income at all. In this regard, it has to be considered a resounding success. It needs work, to be sure and it needs protection but i think the last thing this Government program needs is to be turned over to the forces of the marketplace. It seems to me that the Government has realized it is not sufficient and that is why things like IRA's and 401(K) plans have been encouraged. It is in the individuals best interest to actively save for their retirement years so that those savings can supplement SS, but not necessarily do away with SS altogether. One of the problems with the current system is that people are retiring earlier and living longer. It is quite possible these days to find a person that has been retired almost as long as they were gainfully employed and contributing to the system. Figuring roughly age 20 as the starting point and roughly 65 or so as retirement age, 90 year old people are not nearly as rare as they once were. The ability of the system (and all the similar ones worldwide) to sustain itself with such an increasing and aging population has obviously been hotly debated.
I am assuming that the matter of dividends, interest, gains, etc. is built in... make any assumptions about re-investment, par value, coupons, dividends, etc. and they still add up to a certain return within a time frame for a given security. That's what I'm comparing, head to head... the fully realized return, given the intricacies of each type of security.
The problem i see with this statement is that you include "interest" in with "gains (&) dividends". They are 3 different things that, when one is talking about either long or short term performance, it's important to distinguish between them. Plus, they aren't "built in" and can not be assumed to be so. As I'm sure you have heard before, "past performance is no guarantee of future results". Again, not all stocks pay a dividend, there is no law or requirement that they do so, nor is there any law that says once they start to, they must continue. Some examples are Ford, GE and Microsoft. The first two have been around for about a century, the latter only a couple decades. After all these years on the NYSE, Ford motor company still does not pay a dividend to shareholders (and unless i am mistaken, they never have. If i am wrong, please correct me). GE has been paying one for years and Microsoft pays one also, but it didn't always. Also, the number of companies that issue stock and go public then subsequently fail makes a very long list indeed.
You state in your 2nd paragraph "And if it pays a really fat dividend it could be profitable despite eventually going bust". Well, only if those fat dividend payments added up to more than the initial price paid for the share of the now busted company. Another very rare thing. Companies with publicly held shares rarely start to pay dividends until they have established a history of being able to consistently make money and have succesive profitable years. Both the SEC and the NYSE have rules in this regard (I took and passed a test on this info but it escapes me at the moment!)
If i understand you correctly, i think you are on the right track vis-a-vis "the disaster factor" but you seem to question whether the market has it priced in. I think you might be surprised what the market prices in, and risk, both small and catastrophic are absolutely part of it. But traders do not consider on a daily basis that a Nuclear weapon might go off at the corner of Wall and Broadway nor should they. It is irrelevant. It becomes relevant when a clear threat appears, but for the most part, it isn't. As for the long term, the Social Security Trust Fund is, in my opinion only, best served by being invested in the United States Government, which it pretty much is. We just have to figure a way to make it self perpetuating at a 4 or 5% rate.