1) It's a donation. People who are calling it an investment are incorrect. It's like NPR (I'm sure you hate that)- you donate, and they give you shit as a reward for doing so, but are not legally obligated to give you shit. They are, however, legally obligated to use the money in the way that they say they will.
2) Yes, every project has a goal. Yes, if it's not met, Kickstarter doesn't take your money. Yes, it's possible to take the money and run. You'll notice that Coca-Cola could do that with investor's money as well, there's nothing special about Kickstarter in that regard. Thieves are not exclusively the domain of internet donations.
3 and 4) We've pretty well covered these two, I think.
5) Publishers are a sub-optimal, inefficient way of doing business. Take, for example, this excerpt from an interview with Brian Fargo.
Publishers are responsible for some parts of a project, and they manage to fuck those up with surprising regularity. The Dragon Age Origins trailer with fucking Marilyn Manson over it? Konami not even knowing the release date for Blades of Time? Capcom's constant typos on its products? These are not so common that they are overwhelming, but they are hardly unheard of, and they are indicative of the idea that publishers are not pulling their weight in the publisher-dev agreement.
And sometimes, games that are great new IPs sell far better than expected. Sometimes games that are major releases in established IPs tank. It's really not as simple as saying "new IPs are too risky." They are a gamble, but if they succeed, they earn your company far more respect than another sequel to an old series would, and they give you something new to milk. Someone had to step out and make Call of Duty at one point for us to be at Call of Duty 7.