I suppose no one will ever know for sure exactly how many of the accusations of cruel acts are true but there is one fact that is evident: China prospered under Wu Zetian's rule and it seems the commoners were given more consideration than before. If Zetian had to kill to stay in power... well that's not unlike many many other great rulers of the past. Power hunger is not necessarily a bad thing if one knows what to do with the power when they get it. Plus she was THE ONLY empress in the history of China and she ruled in a time period when women all over the world were pretty much considered less than human. To overcome those odds and make the men of her time know she wasn't to be messed with, she had to be ruthless and yes even cruel.