The SPLC is most famous in conservative circles for being one of, or perhaps the biggest funder of, the hate groups it claimed to fight.
It was so tight with the hate groups that it committed bank fraud to fund them, laundered donor money to subsidize recruiters, and one of its key employees was literally living and sleeping with a white supremacist.
It is also the NGO that helped the left create what amounts to a Stasi that socially, politically, and financially isolated and tried to destroy legitimate conservative groups that were labeled potential terrorists and hence kicked out of the financial system.