You seem to have a fairly good grasp on at least the basics of some economic concepts. On Marx, I would have said I am a "Marxist" myself except I feared it would lead to people jumping to incorrect conclusions (which may still happen now that I've said it). That often happens with economic concepts - people think they understand what a term means based upon all they've heard and experienced, but it's not usually what they think it is. The best example is "communism", which is a term that gets thrown around a lot to mean something it doesn't actually mean. I could spend all day telling people how their perceptions are incorrect, but that doesn't usually work well in a setting like this and will probably generate more anger than anything else.
You get the general concepts I'm trying to point out quite well, such as the idea that luck plays a MAJOR role in how much money you make or what your net worth is. As I said, even the incredibly wealth individuals we interviewed said as much. When they discussed their lives and wealth with us, they discussed it on their own, and then when we presented them with information we'd obtained or determined, they became even more aware of how much random events helped their success.
You are right when you say opportunity isn't the same for everyone. There are many things which affect it that we cannot control, no matter the economic system. However, in our current capitalist mold, those things are emphasized to the point that the distribution of income is widely varied and the wealthy quite literally hold most of the money. This is one of the reasons why the economy is in such a terrible state today. To oversimplify it, middle class spending drives the economy, but THEY are driven by the choices of the wealthy, i.e. if a wealthy businessman fears trouble on the horizon and takes actions which cost many jobs, the people who now make far less money in the middle class (who lost those jobs) have less to spend. When this happens on a large scale (such as recently in 2008 and 2009 as a large example), middle class spending goes down because they have less to spend - but it all started from the top. If the wealthy spent more money in general (on a large scale), but especially on expanding business opportunities and hiring of jobs that provide middle class incomes, the economy improves.