Um, the Black Ajah serves the Dark One. They're assassins and more; whatever they need to be, in serving His purpose. They're not nice folk to have a cup of tea with....unless it's forkroot, of course.
And
please don't ask me to explain that, 'coz I won't.
And I'm not yellow, you hear!
*rips a Gateway with the True Power to wherever Leisha has gone*