A redditor called BobA841908 lays out a lucid and compelling case for how SOPA came about and what might stop it:
A full blackout is a reasonable response, because, in the language that is so popular with politicians, SOPA is going to result in excessive regulation that will cost jobs and likely cause significant increases in the cost of services, perhaps to the point where those services will no longer be able to provided on an ad supported or free to consumer basis.
The only impediment is how to make this coordinated. For instance all the Google, Bing, and Yahoo are going to have cooperate. Otherwise any blackout may simply result in loss of customers for one service, not a clear message to call one's representative. I suspect that if the services choose a minute during the day when no results are returned, only a message to call your representative and state your opinion on SOPA, the bill will die. If Google and MS tell users that search will die if SOPA is passed, no amount of politicking will be able to counteract that message. Anything less is a show of support for SOPA by the major players.
You can't combat piracy. Externalities are a cost of doing business. Anyone who thinks otherwise is kidding him/herself.
There's exactly one way to maximize profit, and that is to deliver a product that people are willing to pay for at a price that they are willing to pay. The pirates were never your customers and never will be, and the sooner the companies accept that and focus on the real problems (massively overpricing everything when first released, delivering products that can't easily be moved between devices because of the restrictive/broken DRM, and the declining quality of entertainment products in general), they'll have better profits. That's not what SOPA/PIPA and similar legislation are about, however. They're about eliminating legitimate lower-cost competition.