E.g., suppose Facebook's equity takes a significant decline in value on the public market: employees become unhappy as the equity component of their compensation declines; Facebook's ability to make large acquisitions becomes more expenseive when its stock is worth less; and its ability to raise capital diminshes because it's more expensive to borrow exactly because their financials aren't as good, according to their stock price.
I personally believe that the long-term goals of investors and founders are very well-aligned. I believe that the common statment by founders nowadays, that they are building a company not for their investors but for their users, will produce the long-term financial results that investors want. It's the short-term goals of investors that conflict with that.
In short, equity isn't this isolated thing that can be happily ignored. It's tied to everything.
So Zuckerberg cashes out at Facebook's peak, leaving the subsequent 'investors' with nowhere to go but down. I wouldn't necessarily put that intention past Zuckerberg, and perhaps a Facebook collapse would be a good thing for openness and interoperability on the web, but isn't it a bit of a self-defeating strategy? Can the hype machine generate enough naive investors to generate a substantial cash-out?
In many ways, for the man on the street Facebook isn't a good investment. At the same time, it doesn't seem to be a goal of management to create a company that entices investors. See the line "we make money to create a better product, not create products to make money."
Doesn't that say it all?