There's no actual fiduciary duty to maximize shareholder value (though a few cases in the early 20th century said otherwise). The fiduciary duties of a public corporation are a lot more narrow, mostly involving not prejudicing some shareholders at the expense of others, or enriching the officers at the expense of the shareholders. Making unprofitable market decisions out of principle (even if misguided), however, is not a breach of fiduciary duty. For that kind of run-of-the-mill disagreement over how to run a business, the shareholders' remedies don't lie in the courts, but in their control over the board. Courts in the past few decades really aren't interested in second-guessing strategic/policy/market decisions, certainly not getting into stuff as detailed as whether Google could choose to ban malware ads, for any definition of "malware" they choose.