Fear is not a sustainable motivator, yes it might give you a short term bump in productivity, but in the long term is kills performance.
Fear causes doubt, it makes people worry, it makes them think about what will happen if they fail, and where your thoughts go your efforts go.
Fear will end up causing procrastination and finally hampering productivity.
Motivation away from something, which is what fear is, is significantly less effect than motivation towards something better.
Creating a positive vision, and sharing the positive benefits of achieving that vision is more motivational. Focusing on building peoples self esteem with positive feedback will always achieve better results. What gets recognized gets repeated, so recognition encourages your teams to do more, to achieve more.
Fear diminishes their willingness to be involved, there willingness to repeat the experience. People look to escape fear, not embrace it and use it as motivation.
Good leaders know this. Good leaders look to create positive environments, develop positive attitudes because they know this will generate positive results.