The Dept is not interested in the opinions or beliefs of US citizens. Our jurisdiction only extends to actions... and only when those actions violate the law.
When Stone appointed J. Edgar Hoover as Acting Director of the Bureau of Investigation, he instructed Hoover to adhere to this standard:
The activities of the Bureau are to be limited strictly to investigations of violations of law, under my direction or under the direction of an Assistant Attorney General regularly conducting the work of the Department of Justice.
Nevertheless, beginning in the mid-thirties, at White House direction, the FBI reentered the realm of collecting intelligence about ideas and associations.