The kinds of concerns which the FBI is using to identify these potentially dangerous citizens are not the hallmarks of dangerous extremism. They are mostly reasonable concerns over the current state of our government held by tens of millions of fairly ordinary citizens who have legitimate reasons to be dissatisfied with government. They are also the same kinds of extreme views which were held by our founding fathers.
The one genuine, unifying characteristic of all of these "extremists" is that they are not happy with a government which is spending beyond its means, taxing beyond our ability to pay and which encroaches more and more on our constitutionally guaranteed rights every day. In their statement the FBI is not actually identifying a real threat to public safety or to citizens, they are sending a warning that public expression of justifiable anger at the government can get you labelled a dangerous criminal or even a terrorist.
This is a tactic intended purely and simply to intimidate and silence the public. They are sending the message that protest is a crime and speaking out against government will not be tolerated. As they did under Hoover, the FBI is categorizing people and making lists and if you don't watch your step they'll put you in a database and take away your rights.
The implications of this statement from the FBI are particularly ominous in the wake of efforts in the National Defense Appropriation Act, the PATRIOT Act and the pending Enemy Expatriation Act to empower the government to take away the most fundamental rights of citizens.
The goal may be to intimidate critics of government, but they are also showing us why we so desperately need to take our government back before these threats of abuse of power turn into full-fledged tyranny.