Alternate systems have not worked out so well, as you know. Communist planned economies led to the starvation of tens of millions, and that number increases to hundreds of millions when you add the persecution, jailing, and sometimes immediate execution of citizens of Communists states that had a history of political activity of the wrong sort. Recall that in Soviet Russia it was beneficial for each individual to "inform" on their neighbours to the KGB, so that they could claim their apartment. And it's suspected that Vladmir Putin is actually the richest person in the world.
Colonialism and slavery are pretty rough, but they are not a product of capitalism as much as a product of human malevolence and brutality. I'm sure you would find evidence of colonialism and slavery in pre-civilization times and in non-capitalist societies, so that argument falls flat.
Also, regarding the 8 richest individuals - If the rest of the world is getting on OK, why should we not have a couple of super rich people around? Why is that inherently bad? Why do _you_ think you should have a say of where that money belongs, exactly?