Elon Musk is using his companies to pursue his personal idealistic goals: He wants to move the world to renewable energy, and he wants to establish a colony on Mars to preserve the human species. Does that mean he's unfairly taking advantage of Tesla stockholders? No, and here's why:

1. There's no single formula for maximizing shareholder value.

In the U.S., we generally believe that publicly-held firms are to be managed for "shareholder value" (technically, the Securities Exchange Commission's Code of Ethics for CEOs only requires the firm to provide full, fair, accurate and timely financial reporting, and to flag any known conflicts of interest or violations of securities law, but state laws often impose stricter fiduciary duties on the firm's top managers).  The hitch here is that there isn't a single definition of what shareholder value means. Though it's often measured simply as total shareholder return, in reality shareholders want different things. They have different preferences regarding risk and return, and they have different time horizons for holding the shares. A large portion of Tesla shareholders own the stock because they believe in Musk's mission, i.e., part of their value comes from the idealistic goals.

2. Elon Musk is the biggest shareholder by far.

Elon Musk holds 33.6 million shares of Tesla stock (roughly 20 percent), which is almost double the share held by the largest institutional shareholder (Fidelity Management and Research Company, with 19.2 million shares), and more than one hundred times as many shares as the next largest individual shareholder (Jeffrey B. Straubel, Chief Technology Officer of Tesla, with 326,237 shares). I think most people would agree that holding 20 percent of the shares entitles Musk to some input on what value is being maximized.  

3. Elon Musk has been extremely honest about his intentions.

Has Tesla sometimes missed the mark on its production or profitability estimates? Yes. Does Musk himself sometimes wax overly optimistic on the company's performance? Absolutely. But Musk has always been extremely honest about the company's goals and his personal motivations. He has also been remarkably honest about the risk involved, noting, "I didn't really think Tesla would be successful. I thought we would most likely fail. But if something's important enough, you should try even if the probable outcome is failure."

The most recent announcement that Musk will take no compensation from Tesla for 10 years, and then will only be rewarded only if the company achieves a market valuation of $650 billion (more than 10 times the current market valuation of General Motors) suggests that either he now believes Tesla will ultimately be wildly successful, or that he's willing to work for the company for free for at least a decade. Both are probably true.

Musk knows that the board of directors of a publicly-held firm may constrain his ability to pursue his goals. This is why he has resisted the urge to take SpaceX public (even though it would restore a massive amount of wealth to him personally). As he wrote in a letter to his SpaceX employees, "Creating the technology needed to establish life on Mars is and always has been the fundamental goal of SpaceX. If being a public company diminishes that likelihood, then we should not do so until Mars is secure." He has also expressed some regret that he had to take Tesla public in order to raise capital to build the company, noting in an interview with Rolling Stone, "I wish we could be private with Tesla...It actually makes us less efficient to be a public company." 

Most Tesla investors likely recognize Musk's idealism and are willingly on board. If there are Tesla investors out there who do not realize that Musk is a man on a mission and that mission isn't just about money, they just haven't been paying attention.