Like any powerful new technology, Americans understand that AI could be used for good or bad. There is optimism on some fronts — but pessimism outweighs it today. Most Americans do worry AI models will act on their own to harm people, and even more that models will be used by people to harm others.  Yet Americans do not want to stop AI altogether, because most do think the U.S. needs to develop AI to be competitive, and must do so faster than China. They also think that it can lead to medical and scientific breakthroughs. So it's a matter…