They're upset because they like the status quo. They like the good trade advantages. Why would they like someone that challenges them and wants to reset trade to make it more fair?
China's been steeling the world's technology for over 30 years. If you want to do business in China, you have to have a 50/50 joint venture and agree to give away your intellectual property, including patents and know how. Military technology is stolen each year through China's cyber agencies. The world should be the one upset with China and not the other way around.