That's not true.
ETA:
linkie to FBI page:
Public Outreach: The FBI has forged partnerships nationally and locally with many civil rights organizations to establish rapport, share information, address concerns, and cooperate in solving problems. These groups include such organizations as the American-Arab Anti-Discrimination Committee, American Association of University Women, Anti-Defamation League, Asian American Justice Center, Hindu American Foundation, Human Rights Campaign, The Leadership Conference on Civil and Human Rights, National Association for the Advancement of Colored People, National Center for Transgender Equality, National Council of Jewish Women, National Disability Rights Network, National Gay and Lesbian Task Force, National Organization for Women, Sikh American Legal Defense and Education Fund, The Sikh Coalition, Southern Poverty Law Center, and many others.
(emphasis added)
Here is their page on Charles Murray who they criticize as a White Nationalist (hey, what's wrong with that?).
Ayaan Hirsi Ali - how is she not an anti-Muslim extremist?
Here is their write-up on Maajid Nawaz, including "But major elements of his story have been disputed by former friends, members of his family, fellow jihadists and journalists, and the evidence suggests that Nawaz is far more interested in self-promotion and money than in any particular ideological dispute. He told several different versions of his story, emphasizing that he was deradicalized while in Egypt — even though he in fact continued his Islamist agitation for months after returning."
The Southern Poverty Law Center does present documentation for what they say - afterwards you can disagree with the conclusions they draw if you wish.