Sylvanas isn't an outlier. She is a representative of Forsaken society

I mean she basically invaded Stormheim and almost enslaved an entire race just to meet her needs. I can't say that's a peaceful thing to be doing.

She did it to "save" the Forsaken.

She had taken her flagship, the Windrunner, to Stormheim in the Broken Isles, in search of more Val'kyr to resurrect the fallen. It was, thus far, the only way Sylvanas had found to create more Forsaken. "I was almost able to enslave the great Eyir. She would have given me the Val'kyr for all eternity.** None of my people would have ever died again." She paused. "I would have saved them."**