I understand where you’re coming from and I’m a believer in karma but if Red China beats up on Japan, the world would be worse off. We cannot judge the geopolitical situation of 2013 by 1931 standards. Japan is a horse of a different color now and a strong ally.
The Chinese aren't exactly choir boys - every change of dynasty in China involved the deaths of tens of millions, many executed the old-fashioned way, with edged weapons during post-siege massacres. And then there's this account of the Chinese treatment of the Dzungars, during which they were more or less exterminated:
According to Qing scholar Wei Yuan, 40% of the 600,000 Zunghar people were killed by smallpox, 20% fled to Russia or sought refuge among the Kazakh tribes, and 30% were killed by the army. Clarke has argued that the Qing campaign in 1757-58 "amounted to the complete destruction of not only the Zunghar state but of the Zunghars as a people." Historian Peter Perdue has attributed the decimation of the Dzungars to a "deliberate use of massacre" and has described it as an "ethnic genocide". Mark Levene, a historian whose recent research interests focus on genocide, has stated that the extermination of the Dzungars was "arguably the eighteenth century genocide par excellence."