He's no different than any other shareholder. You guys get way too upset over his "greed" while ignoring the fact that every shareholder of every company wants exactly the same thing.
Okay, maybe in Apple's case there's a lot more fanboys who own stock because they love Apple and don't care at all what the stock price is. Those types may be more prevalent on forums like this, but they're definitely not in the majority and they're not good shareholders because their lack of interest in profit hurts what is fundamentally a profit-making venture.
It's not like Icahn is a major shareholder, either. His stake in the company, while large in absolute terms, is tiny in relative terms. He's not going to be listened to by the board of directors or anyone else at Apple any more than any other active shareholder. Nor is his proposal binding. He literally has no power except to talk. If anything, his proprosal shows that he's made no headway through any of his prior attempts at getting Apple management to change their minds about current policy. For those concerned about his influence, this proposal merely demonstrates that he has none.
If he were to dump his stock suddenly, the price might take a slight dip, and then other investors would eagerly buy up the shares again because, as AAPL has been for quite some time, they'd be undervalued on the market. He can't cause a crash. He can't cause anything. Apple is much too big a company for him to hurt in any way.
That all said, he's completely right that AAPL is undervalued, and Apple should be doing buybacks with their cash. They don't seem to be able to spend it quickly enough on their own since it's just piling up, and a buyback would, among other things, increase shareholder value. Note that this doesn't increase just Icahn's shareholder value, but everybody's (except those who sold their shares back to Apple, of course). It will increase demand for the stock because earnings will be spread over fewer stock, and the stock price will go up. Apple will be in a stronger position going forward because they can probably buy the stock back with debt, rather than their cash reserves, as they did with their recent dividend payouts, which had some significant tax advantages. Apple will also be able to raise capital more easily in the future should they have a need. Whether Apple's existing plans are good enough, or Icahn's plan is better, it's up to Apple shareholders to decide, and act accordingly. For now, though, it's in Apple's hands to act on shareholder sentiment or not. If the shareholders don't think Apple is doing a good job, they can vote out the board, or simply sell their shares which will cause a far greater drop in price than Icahn ever could do alone.
Right now much of Apple's cash reserves are doing absolutely nothing for Apple the company or Apple's shareholders. It certainly won't make anything worse giving back more of that money to shareholders, and it will give Apple's shareholders the opportunity to spend that money in other ways. It is the point of corporations to make money for their shareholders.
So, if you find yourself having an opinion on this, you probably fall into one of three categories. Let me address you all accordingly.
If you're a shareholder who's interested in money, Icahn's proposal is worthy of serious thought. Whatever your opinion, it's perfectly valid, and you should act in your own best interests.
If you're a shareholder who's interested in Apple's products, not in money, please sell your shares to somebody who actually cares about money. You are a bad investor.
If you are not a shareholder, nobody cares what you think. Please go away.