The best way to approach it is to ask them questions. It's best if you can get them to create answers that lead towards a Marxist approach.
For example: "What would happen if everyone was employed?" The should lead to a discussion about over-production, though you may have to ask, "Well, if everyone had a job, wouldn't they produce so many goods and services that they couldn't all be sold? What would happen then?" Try and lead them to the conclusions, instead of telling them the conclusions.
The Socratic method. Socrates would ask people series of questions to get them to see things his way. People like to convince themselves of things.
"As soon as the land of any country has all become private property, the landlords, like all other men, love to reap where they never sowed." -Adam Smith
"If you want a picture of the future, imagine a boot stomping on a human face -- forever." -Orwell