One reason not to do that is to hide your methods. The usual tactic to show good anti-terrorist results is to inject provocateurs into fringe groups and paint them as thwarted terrorists. I hope that US is not going that route.
Most of the Islamist terrorist plots federal authorities have 'broken up' over the past twenty years have involved undercover agents leading on people who are too dysfunctional to be dangerous to do things for which they can be convicted.
