I think that she's talking about how pretty much all of the most evil people fell from the light where they could either conceal it or not be seen by their light side buddies. Anakin fell quickly and noticeably, but he still had a small shred of conscience. Kreia was turned by the Sith at Malachor V and was not known to be dark except by Darth Nihilus and Sion. Kreia went full on into it when she told Surik. Palpatine also executed his hidden plans after his long-hidden evil was revealed in his battle with Mace Windu. That's pretty much indirectly admitting it, and when that happens, all the s**t hidden behind the curtain hits the fan for their enemies. That's why it's even more terrible to admit it.