The FBI's role in rounding up Japanese Americans during WWII and hunting down "Communists" in the U.S. is also shameful.
Actually, the FBI had nothing to do with rounding up Japanese-Americans during the war. The Bureau did arrest and detain enemy aliens (non-citizens, including Germans and Italians as well as Japanese), but the FBI and Justice Department had nothing whatsoever to do with the rounding up or internment of Japanese-Americans. In fact, both resisted the move to deport Japanese from the West Coast, which is why even this flawed film goes out of its way to have James Stewart in his narration state that "These were enemy aliens, not loyal Americans of German or Japanese descent." The fact is J. Edgar Hoover opposed this "relocation" policy, which was championed by, among others, Earl Warren, then Attorney General of California and later the Chief Justice of the most progressive Supreme Court in history. But during the war Warren was one of those "shameful" people, including a great many liberals, who was among the loudest voices demanding Japanese internment.
As to "hunting down 'Communists'", Hoover was obviously a zealous anti-Communist, but the fact is there were Communist spies working for the Soviet Union engaged in espionage activities against the United States. Why would you have a problem with arresting spies? And yeah, in the postwar period they were actually Communists.
There's a lot to criticize in this movie and about Hoover and the FBI, as the OP's post points out, but not what you cited, which just indicates a profound ignorance of history.