Fallen human nature and the economy

I read an article by Christopher Mannion and he mentioned fallen human nature and communism.
And then I remember the arguments from mixed economists and socialists that capitalism is bad because humans are imperfect and will eventually abuse the system.
Made me wonder, if communism or capitalism can't be implimented because of fallen human nature, how can a mixed economy be the best? Seems like the worst of both worlds.
So, it makes sense to me that capitalism is the least destructive economic system. If abuses are going to happen, at least it provides the most capital and the most in demand goods for reasonable prices.