Remember, Stark Industries is a defense contractor, and thus subject to the same regulations as a company like Lockheed Martin. Any technology built while on a government contract can be used only on that contract, whether it be a tank engine or a piece of software. Because, you know, the government paid for it. The developers can't sell the technology to anyone else or use it to destabilize foreign terrorist cells on a lazy Sunday afternoon.
And as we know from the first Iron Man movie ...
... Tony built the original Arc Reactor -- the one thing that makes the suit work -- as part of a government contract. Hell, the original armor prototype he threw together in the cave was built out of parts from missiles he created under another defense department contract. All of that research and development was done on the taxpayer's dime, and then Tony uses it to turn himself into a superhero and claims that nobody else has a right to put their filthy paws on it. In reality, it would be illegal for Tony to use an Arc Reactor to power his goddamn TiVo, let alone use it to fly halfway around the world and punch tanks in half (which incidentally is also illegal, because crossing national borders with that suit constitutes the trafficking of defense technology).
But knowing that he's in violation of federal law every minute he spends zipping around in his futuristic explosion suit only makes his other decisions that much more baffling.
We're not even including his facial hair and choosing to date Gwyneth Paltrow.