There are white racist 'agitators', too. Farrakhan gets a lot of media play because he's been around forever and is more interesting than most other racist agitators. He's black, and he's Muslim, for example.
As a "liberal" I say this is supposed to be a free country, and these racist agitators have a right to speak their mind just as anyone else does. And just as we have a right to ignore them. Or to speak our antipathy.
It's better to know who they are and what they the ink than to force them 'underground' where these ideas can fester unseen, until they explode into cultural violence.