It's a foregone conclusion that governments can -- and in some cases MUST -- influence markets, and the reverse is also true. But there is still the trend among capitalists to prefer the market to have more influence over the government than the reverse, and where this has been easy to accomplish -- in central and south america, for example, where the capitalist class controlled considerably more wealth than the governments of those countries -- the result has been consistently disastrous.
Central and South America weren't capitalist (by our example), as they had a ruling class or ownership class which excluded the vast majority of people from membership. They're closest to French merchantilism under the old monarchy.
As Hernando De Soto pointed out, these countries flip between ruling juntas, "business" leaders, socialists, and quasi-Marxists, and nothing
actually changes except who you have to bribe.
Don't confuse capitalism with stock markets. American capitalism is the result of letting everyone
buy, sell, and own land, businesses, or products, which are rights not recognized (or overly regulated and restricted, such as making peasants spend twenty years bribing officials to get a deed to your own house and a license to hire people to sew buttons on shirts) throughout much of the non-Western world.
Socialism only works to the extent it's not
implemented, which is one reason why Western Europe scaled it back dramatically. As Margaret Thatcher observed, socialism works until you run out of other people's money (and then you're screwed).
The reason socialism never systematically fails is because it is never systematically implemented. At their cores -- where they relate to one another, at least -- capitalism is an economy controlled by private investors while socialism is an economy controlled by the public. The fundamental difference between them is where the money comes from: in pure socialism, all investments are made collectively through the the delegation of tax dollars, while in pure capitalism all investments are made voluntarily and individually.
Under socialism you replace 300 million very engaged brains with a mere hundreds of brains, which is why it always fails. Collectively, people are as dumb as crowds, and there's no way around the problem that the people who step up to think for them them will be the power-mad, narcissistic, Dunning-Kruger idiots. It's an information problem, and no government can collectively process all the information of free people conducting transactions on an hourly basis. It's like thinking you can beat the complexity of a rain-forest ecosystem with a top-down management
policy that dictates tree height.
Purely as a matter of political efficiency and economic growth. Iraq was a rich country under Saddam. Miserable and terrified, sure, but they did experience fairly steady growth and prosperity until they got their asses kicked in the Gulf War.
Iraq was a very poor country, dependent on oil revenues handed out by the government, which didn't have much interest in passing the revenues around very freely. We've all seen the pictures. It was a third-world socialist hell-hole with a dysfunctional infrastructure, intermittent electricity and non-existent sanitation. When we invaded, the people there talked about how they remained frozen in the 1970's, as if the world slowed to a stop as Saddam and the Arab socialist Bathists took power. Saddam's inspiration was national socialism and communism. He should've known it wouldn't end well.