Paul Harris reports in The Guardian that FBI tactics are raising disturbing questions of 'entrapment':

Civil liberties groups are also concerned, seeing some FBI tactics as using terrorism to justify more power. "We are still seeing an expansion of these tools. It is a terrible prospect," said Mike German, an expert at the American Civil Liberties Union and a former FBI agent who has worked in counter-terrorism.

German said suspects convicted of plotting terror attacks in some recent FBI cases bore little resemblance to the profile of most terrorist cells. "Most of these suspect terrorists had no access to weapons unless the government provided them. I would say that showed they were not the biggest threat to the US," German said. 

"Most terrorists have links to foreign terrorist groups and have trained in terrorism training camps. Perhaps FBI resources should be spent finding those guys."

As Harris points out, there is a clear pattern to the FBI's "success" in thwarting terrorist attacks in the United States:  the idea, the money, the weapons and the plan all were supplied by the FBI working through a generously paid (often criminal) informant.  It's pretty easy to conclude these individuals probably would have done nothing without the encouragement of the FBI.  You can read about recent FBI operations here, here, and here.