I don't understand the down vote. People actively choose to back projects that are past 100% funding. This means they want to participate. Setting an arbitrary limit in order to protect people seems ridiculous when the information about funding levels is right there, in real time. How is contributing when the project is at 150% funding any more risky than when it is at 50%? You are still in for the same pledge amount.

The only legitimate concern I could see is that by allowing projects to fund well over 100%, you're potentially increasing the risk to all backers as an easier to manage 12k project balloons into a very complex and potentially hard to manage 200k project.