Firstly, I am largely pro-capitalism. I think it's generally good for growth and responsiveness to consumer needs and desires. However, I think people can get a bit unrealistically dewy-eyed about capitalism.
If the likes of Enron, the banking collapse, or even people like Madoff and Conrad Black have taught us anything, it's that capitalists can screw the place up as well as anyone if they aren't being watched over very carefully. Top businessmen can behave like tyrants, arranging vast benefits for themselves whilst the bulk of their workers get nothing. I read some top execs in the UK had a deal going where the company paid for all their transport costs, by which I mean even their own, personal travel. Why, as a shareholder or a worker, should I have my earnings limited so that someone who earns 200 times what I do gets a load of his personal, non-business expenditure covered by the company? Why should I pay proportionally more tax to the government than someone who earns 200 times more than I do, just because the company arranges his remuneration so that most is non-taxable? Why should I get taxed 30% of my income for my hard work, when some guy doesn't do any work and inherits several times my lifetime earnings tax free - how is that "rewarding" work? And yet vast amounts of media inches and internet forum databases are full of people complaining about welfare scroungers, with very little attention being paid to the fact they are getting screwed from the other direction.
Capitalism is also massively dangerous to egalitarianism. Even 300 years ago or so, John Locke realised that vast wealth imbalances cause social disorder and inherent inequality.
Imagine a system whereby a minimal state only provides the law, law enforcement and the army. It's pretty much true that the more you spend, the better you'll get of something. Let's consider education. Poor parents could only afford worse (if any) education for their kids, this would severely impair their ability to be successful. You'd simply lock a cycle whereby the poor and their descendants stayed poor, whilst the rich stayed rich. They'd also be impaired by worse healthcare, and whatever else they couldn't afford. In such a country, there's not even any meaningful equality of opportunity.
Currently in the USA, the top richest 1% of the country's population owns about 40% of the USA's total wealth; the top 5% own about 60%. Wealth is often dependent on wealth - you can't make money via investments (property, shares) unless you have the wealth to invest in the first place. This also makes it easier for the rich to stay rich, and harder for the poor to become rich.
Also importantly, consider the role that wealth plays in politics. One rich man can fund a massive campaign single-handedly; a poor man has to convince thousands, hundreds of thousands of people to back him before he even runs. In any developed country, the legislature and executives are massively and unrepresentatively full of people who were independently wealthy before they entered politics, and most of them were from wealthy families, rather than being "self-made". It stands to reason many of them will legislate with the interests of themselves and their social circle in mind. If they are being bankrolled heavily by a few individuals or organisations, we could reasonably consider them "bought" to represent the interests of those individuals. In this sense, the nation is at risk of increasingly representing an oligarchy or plutocracy, where the government acts in the interests of the privileged, rather than the population as a whole.
Capitalism needs to be clamped down on in many areas.