Fiduciary duty to shareholders. A blackout preventing searches (rather than an informative message that users can easily dismiss) would impact revenue and might result in a shareholder lawsuit. Not to mention the impact to AdSense [edit: I meant to say AdWords] advertisers who might see that as an SLA violation.

Does AdSense have an SLA? In any case, I'd be shocked if the contracts weren't in terms of number of searches. If 0 searches are done, there will be 0 AdSense "hits".

The "fiduciary duty" to shareholders seems pretty far fetched and could be argued the other way as well. Enforcing SOPA will be a heavy financial burden and negatively impact future performance, therefore not using every means necessary to block SOPA is also a breach of "fiduciary duty".

I completely agree that it could go both ways. However, anybody can sue for anything these days. While opposing SOPA is the responsible choice, I can see a potential shareholder suit claiming that opposing SOPA could be done without taking drastic measures (ie: a blackout rather than a dismissible message) that immediately impact revenue.

Reddit also has shareholders, even though it is a private company. Fiduciary duty obligations apply to Reddit management as well. IMO, management at these companies would have a very strong argument that opposing SOPA in dramatic fashion would be more likely to increase shareholder value in the long run.