Spread of privatisation
Opitz told Reuters news agency: "What really bothered me before starting this was that everyone said you can't do anything about the spread of privatisation, even though it affects so many people in such a fundamental way.
"If people are informed about the potential impact of privatisation on healthcare, railways, power suppliers and still want it, that's their choice.
"But they're usually left in the dark. My aim was to show privatisation's impact on people."
While insisting he is anything but a fan of Michael Moore, the US filmmaker, and his confrontational approach, Opitz's English-language film Der Grosse Ausverkauf - as it is titled in German - is similar in style.
Featured in the documentary, Simon, a British train driver, says he once worked for the most efficient railway system in Europe, but since its privatisation, it has become run-down and dangerous.
"Privatisation has become such an unchallenged ideology," said Opitz, who spent four-and-a-half years on the film which has financial backing from German public television.
"It is not a law of nature. Too many people shrug and say 'What can you do?'"
In another segment of the four-part story, a poor mother in the Philippines struggles to raise money for the dialysis her son needs.
In the end, hospital staff tells her she should just accept that she cannot afford her son's treatment and let him die.
The third story is about a South African activist and his "guerrilla electricians" who risk their lives helping families illegally re-connect their power after a privatised electric company switched it off over unpaid bills.
The fourth story is about violent protests in Bolivia in 2000 that accompanied - and prevented - attempts by the local congress to impose charges for water they had received free.
"Sell now, pay later - our world is being privatised," said 34-year-old Opitz.
"This looks behind the abstract idea of privatising basic public services."
He said: "Who will have access to water, energy, public transport and healthcare? Only those who can afford it."
Opitz's film has been featured in festival screenings in Toronto, Chicago, Berlin and Hong Kong.