Child porn is how .au passed their censorship stuff and it has quickly expanded. Child porn is already illegal and, in my opinion, doesn't need deep cutting censorship bills to combat.
"So if a company starts infringing trademarks, polluting search engines en masse, tricking people into buying their rubbish"
eBay? also, already illegal based on trademarks, copyright, etc etc.
"What about people who DDoS attack you? Is that fine? No need to have any recourse there?" "How about those that hack DNS to dupe people into visiting their site etc"
already illegal
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from my understanding, SOPA is more about removing due process than making bad things illegal