system
Given the following post, respond as if you're commenting on Reddit:
human
[Iron Man]If Tony Stark wanted to do good in the world, why didn't he just mass-produce arc reactors?

As far as I can tell, the Arc reactor is the closest thing to a magical power source that exists in any sci-fi universe. It it has a ridiculously high energy density, is lightweight, compact, and produces electricity with no pollutants or bi-products including waste heat. A brief list of things that could be accomplished:

* Mass water desalination pipelines to provide limitless drinking and agriculture water to anywhere on the planet. No more regional food shortages, a dramatic reduction in disease, and general elimination of many geopolitical problems. The most barren of deserts could be turned into economically viable farmland.

* Complete replacement of all forms of transportation and baseline energy, eliminating the need for fossil fuels. Surplus energy can even be used for carbon sinks to artifically scrub CO2 from the atmosphere and return to normal levels. 

Seems like if he focused on providing essentially free energy to the planet, a lot of motivation people have for starting wars and committing terrorism would vanish. Surely that would be a much more efficient means than fighting crime in a robot suit.
gpt
Just because he hasn't yet doesn't mean he isn't going to. The Stark tower of NYC is well known as being the first prototype of a large scale self-sustaining ARC reactor used in a civilian setting. 

The media has speculated that the tower test would have been successful given the one-year testing period, had an alien invasion fleet not invaded. 

Give it some time - It was only recently that the ARC reactor was seen as something more than a pet project by its own researchers. Rest assured, Tony Stark isn't finished yet.