But anger at perceived injustice is a pretty universal human emotion (based on my general observations).

My looking at history is that this isn't quite correct. It is the most restrained aggressor/tyrant who winds up getting targeted. To use an example I'm familiar with most of the Russian Tsars were rather despotic; however, two did make major liberal reforms, Alexander II freed the serfs, and Nicholas II make strides towards modernizing the country including introducing an elected parliament. Not-so-coincidentally, they were also the only tsars to be assassinated by revolutionaries.