What she said was poorly worded, but it's not what you're making it out to be. She was not saying she wanted to exterminate black people. She was saying she didn't want people to get that idea. And yes, unfortunately she did have some very bad beliefs. But she also did a lot of good fighting for access to birth control, which was illegal at the time.
If she really wanted to exterminate all black people, why did she have support from a lot of black people at the time?