the 'business interest' rhetoric is a bit off. this isn't about business, this is about copyright holders (businesses just so happen to hold a lot of copyrights). it will empower small and big copyright holders alike.
you might also mention how this issue has been framed ('theft of intellectual property' - piracy etc is not theft it is conversion, an infringement of property rights)
you might also mention the acronyms. Stop Online Piracy Act - it won't stop online piracy considering it doesn't punish pirates, and won't work : 1) linking to pirated material etc will just move to foreign sites, and 2) foreign sites can only be DNS blacklisted, which can be circumvented with minimal effort. if you want pirated material you can still get it.
you might mention louis c.k.'s success (though it has limited application to the wider issue) in low cost, accessible original content.
you might also question the values of the scumbags who are trying to push this through, like chris "i promise i won't be a lobbyist after i resign from congress" dodd (now head of Motion Picture Association of America)
the wikileaks example is a bit of a non-issue. determined web denizens will still access the site, and you are wrong in saying that the US can 'shut the site down'
to be quite honest a lot of the arguments about economic growth and being a content provider or crowd-based site like reddit are shit. "SOPA would make running Reddit near impossible" is another way of saying your business model is based on infringing copyrights. its like saying i can't run my restaurant without cockroaches and rats everywhere
you might also mention how
fluoridation is one big conspiracy and therefore SOPA and PIPA are bad