One can certainly point to bad things some humans have done, but that seems like less a fundamental characteristic of the species and more like the squeaky wheel getting the grease. On the other hand, ponies are familiar with the concepts of war, tanks, bullets, and guns, and pre-Equestria the three pony tribes showed a great deal of racism and political turmoil, only learning to accept one another when they had to choose between tolerance and a slow extinction through starvation.