Mao being a psychopath got shit done, and his victims are footnotes in history books when anyone bothers to mention them.
Conquest requires traits deemed "pathological" by the losing side. In other news Genghis Khan, Tamerlane and and Alexander the Great also imposed their will violently on countless forgotten "NPCs" who were replaced with little fuss.
Just because something offends someone else's arbitrary subjective "morals" is no reason of itself not to do it nor does it make that choice strategically counterproductive. To call something "immoral" is a fancy way of expressing dislike, usually accompanied by pearl clutching. That technique impresses the weak which Mao was the opposite of.
Xi is not going to attack the "civilized world" but may attempt anschluss of Taiwan which is not the same thing at all. Xi follows the old early Cold War playbook which now works reliably to frighten moderns not familiar with thus jaded by the old ways.
Xi is counting on scaring the ignorant but one does not rise in that system without being a team player and the CCP show no historic evidence of being suicidal. The US may or may not be inclined to spill blood and treasure for a weak client whose self-defense efforts relative to its enormous wealth are not impressive.
Taiwan is not a beacon of freedom and democracy, it's a business on an island which the early Cold War gave exaggerated importance. Taiwan spends little (only 2.5 percent GDP) on defending itself, preferring US military welfare. https://globaltaiwan.org/2023/...
That's not how serious people prepare to deter an existential enemy. Xi knows this.