I'll try to explain this as simple as possible.
If Kickstarter says you set a goal for backers and if you don't reach that goal, you don't get funding, it's extremely unethical(hence why it's against Kickstarter's rules) for the person who is running the project to suddenly donate the difference to get their hands on the backers' money. You're pledging with the understanding that the project will get enoughoutside interestto fund it. If it does not get that level of interest, the project does not get anything. If you only needed 300,000 for your project, don't set the goal to 800,000. Etc.