When Japan built its Shinkansen, she had just been thoroughly beaten in a war, and we were reasonably confident she was no longer "bad". We have no such confidences with China; she has proven herself to be "bad" at many times. She is still locking ethnic minorities in concentration camps, continues to try to take over Taiwan, has taken over Tibet, mistreats her citizens, is focused on expanding the surveillance state, and is (in my view) intent on eventual world domination. Whether she will achieve this goal is debatable, but the risk is still there, and having many developing nations beholden to her is a risk for the free world.

At some point, I would argue any nation with more people than the free world in total that also has a totalitarian government is a risk to the rest of us. It's important to bound the influence of China, because should a war break out, the scale of death would be much larger than ever seen before. This is both because of China's sheer number of bodies she can throw at a problem and because of better technology.