If you believe that "intellectual property" is a "thing" (as many people do) then you may consider China's behaviour in this area (obtaining trade secrets illicitly, or forcing companies to reveal them as a condition for doing business in China, or breaking copyright law) to be theft and more than enough grounds for sanctions.
Even if you don't believe in "intellectual property", then you may still believe that a selective (not universal) and one-sided breaking of the relevant international and national IP laws, in favour of one country, is harmful.
In addition to that, there have been allegations (I'm not sure how true they are), that supposedly private Chinese companies have been supported by the Chinese government in ways that break WTO rules.
No one is forced to reveal secrets. Play ball with their rules or don’t business in China. Our own government forced tech companies to do certain things. Why can’t China set its own rules?
Sure I believe in IP. I also think other countries will do as they please when they know they will get away with it. Nation states behave in self interest and can have their own interpretations of what are black and white laws to you or me, especially so when they’re in a position of power. Or they can completely disregard international agreements. Case in point - the Iran deal.
>Play ball with their rules or don’t business in China.
If you don't manufacture in China, you can't compete with companies that do. As a result, every company is forced to sell out their future 20 years from now so that they don't go under today. Whether you think it's a good idea or not, government intervention is often necessary to coordinate industry-wide strategic things like "don't put poison in milk" and "don't take the sweet but deadly embrace of technology transfer."
You simultaneously believe in IP and are confused that American companies are upset by IP theft by Chinese companies? Why would they not be? It's not like they agreed to well-defined contracts trading away their IP. It's reasonable to be upset if you believe the other party in a contract has unilaterally broken it.
Even if you don't believe in "intellectual property", then you may still believe that a selective (not universal) and one-sided breaking of the relevant international and national IP laws, in favour of one country, is harmful.
In addition to that, there have been allegations (I'm not sure how true they are), that supposedly private Chinese companies have been supported by the Chinese government in ways that break WTO rules.