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.