I doubt they would do that to an average schmuck like me, but the fact that it's a common consideration shows how far the Chinese government has fallen in the international public's perception.
It's a shame, too. China has some really great cultural sites, substantial natural beauty, cosmopolitan cities, and excellent and varied cuisine. It would be a great tourist destination under a different government.
I gave you two specific, recent examples of Canadians who were in China and arrested in response to Meng Whanzhou being held for extradition to the US. While she was living in a mansion they were in jail with 24 hour lighting, daily questioning for hours, and being denied to consulate officials. I'm not against China or making a political statement about their domestic policies, but I'm not oblivious to foreigners having no rights there or recourse which is certainly not the case here. As a Canadian the other frustration is this was really a US-China spat and Canada was immaterial.
It's not pervasive. Incredible claims require evidence, which you have none. If anecdotal evidence is enough, dozens of people I know go to China with zero issues regularly. Many people we know live there with zero issues. There's 1.4 billion people, logistically what got are saying is not feasible for a country that size. It's nonsense.
Holding up a blank piece of paper is a completely different scenario and topic! We are talking about normal, everyday travel for business and recreation. If you go there and do something taboo, something that's clearly intended to cause trouble, then what do you expect?
With any foreign country you should understand their cultural norms and laws. Your own ignorance is a valid consideration for travel, not being arrested as a political prisoner. You won't get in any trouble as a tourist or business person 99% of the time.
You're right; the risk of abduction is vanishingly small, even if many people are terrified of the power of the Chinese government. I'll replace "legitimate" with "common" in my comment.
It's a shame, too. China has some really great cultural sites, substantial natural beauty, cosmopolitan cities, and excellent and varied cuisine. It would be a great tourist destination under a different government.