Banning assault weapons is an infringement on Americans freedom to protect themselves; what minor civil liberties advances may be gained pale by comparison to this.  It is also unlikely that the police and the FBI would recognise the linkage between fewer guns in the civilian population and reducing the firepower of the police. Similarly the FBI is unlikely to monitor civilians less simply because there is one less reason. The justification of “preventing homegrown attacks before they are hatched” will still remain just as strong as before they will simply be looking for different things.