One of the major arguments against SOPA is that it's currently vaguely worded. As it is, SOPA allows persecution for websites who have links to pirating websites in their comment features. So, if somebody commented on a Time magazine article online giving someone else a link to The Pirate Bay, they would be leaving Time out to dry and left faced with a fine or other repercussions to deal with.
This brings up another interesting point, The Pirate Bay specifically is one of the largest providers of pirated material. However, it is based out of Sweden. So how can American legislation be made to quell a foreign "threat?" The bill leaves a lot to be desired and is under a lot of scrutiny from a large number of internet companies, so that 9% approval rating could be dropping.
I feel this bill is either a distraction from other difficulties that are happening in America or the World. Congress might be using themselves as a scapegoat (if that's possible) to draw attention away from the Occupy movements. Either that, or Congress realizes that they have nearly no support and decided that they might as well do what they want since they don't have much to lose.
Opposition to SOPA claims that their rights are being infringed upon, even though they're aware that they are harming the entertainment industry by pirating music. The strongest opposition are those who advocate free media, and therefore the sharing of files freely. Their reasoning for this is usually because they don't have the money for it themselves, but use the example of the price of media being a day's wages in less fortunate countries and therefore the content should be free to them.
Now feel free to give your input on this matter.