In context, the GGP is positing that stocks should have a higher rate of return than other modes of investment because, to paraphrase, "companies create value". The point of the GP is that perceived value to investors drives the stock price more than value to society, thus countering the notion that stocks are inherently "better".
first of all, whether or not a company "creates value for society" is a red herring. it doesn't matter to an individual looking for an investment vehicle.
> To an average small investor, shares in almost every company might as well be Magic cards. Their only value is to sell them later to a different collector
this is true to the extent that thinking of stocks this way probably wouldn't hurt you as a small investor, but it obscures the reason why stocks have value and are different from bonds. when you buy a stock, you are locking in a fraction of future real productivity, whether or not you can derive cashflow from it directly. with a bond, you are locking in a nominal return, which could result in a real loss over time. although stocks have significantly outperformed bonds historically, I would hesitate to say that one is inherently better than the other; they just carry different risks.
as an aside, I'm really not sure why non-voting shares that don't pay dividends are valuable, but AFAIK, these are not as common as nrclark suggests.
> Do any of us actually believe that Snap's stock price is reflective of its value to society?
of course not. the stock price doesn't represent the value to society; it represents the (perceived) value to investors, taking into account potential for growth. ford is an established, stable company, but it's hard to see any avenues for massive growth over the next decade. I don't personally believe snapchat will grow massively, but it's more likely than ford to do that or get purchased for a huge amount of money by a tech giant.