Compare USA with Nepal or any other socialist, communist country and try to find out why the USA is so far ahead of them. You think they were lucky? God gave them more or better? Since the early day of Puritans, these immigrants worked hard and within few hundred years they made the modern USA. Capitalism assures you opportunity (but not equal opportunity) with the realism of safety and security, and it's there for somebody to grab it, some make it some do not. It's the law of the nature. If everybody was to achieve A+ in your class, what is the fun? Some are rich, some poor. As long there is an opportunity, it's up to you.
Yet no system is perfect, including capitalism. Plenty of flaws.
Take a look at the recent news, those Arabs who dogged Western Capitalism all throughout their history are finally accepting the reality and marching all across the continent for better equality, freedom and prosperity. They will not achieve any of that if they end up with communism,socialism and extremism.