I think it is instructive that while eBay was able to void the Craigslist poison pill provision in court, they have not been able to, for example, sue Craigslist into increasing revenue and profit by charging a per-listing fee on "for sale" items. To my knowledge eBay hasn't even tried that--no doubt because they know it would be futile.

The practical question is not necessarily whether Craigslist has a duty to maximize shareholder value, but rather, to what extent can shareholders use the courts to second-guess the business decisions of corporate management? As the links in the Google search above attest, decades of precedent seems to suggest: almost no extent at all.

To look at another high-profile example, Apple CEO Tim Cook--in a shareholders meeting!--said "When we work on making our devices accessible by the blind, I don't consider the bloody ROI. If you want me to do things only for ROI reasons, you should get out of this stock." While it made some news, I don't recall a shareholder lawsuit forcing Tim out of Apple for refusing to maximize shareholder value.