Capitalism also requires the approval of government. It's largely through the government that ownership is defined in the first place. Without this, you have nothing to trade.
What is wrong with it? Well, the problem seems to be that those with large amounts of capital can use this to buy time from other people. And, over time, the rate at which the large capital blocks gain wealth is greater than the rate at which the overall economy grows. Eventually, we move into a situation were most of the wealth is in the hands of very few individuals, at which point, they control society and any notion of democracy disappears.
Don't worry about it, though, I am sure it will be a long time before we have such enormous disparities of wealth that we have to worry about this.