Interesting hypothetical. You are saying that people who want tougher anti-crime laws are also in support of the police killing the innocent and abusing the people but I see that as a false equivalency. It seems more reasonable to assume that those supporting tougher anti-crime laws do not support murder and rape and methods for crime fighting and would not support such activity.
The scared grandmother of 80 who wants tougher anti crime laws would reasonably assume that these laws and law keepers are going to not commit murder, rape, and abuse to get the job done. Those people believe in the system which means they also believe that the system will work within its own boundaries and not turn to crime to fight crime.
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I don’t think it’s a good idea to try to extrapolate the general attitudes of Americans from comments posted on BoingBoing. I don’t think this readership is very representative of the people.