Looking into it, the stem cell stuff in Japan is probably because it's the
largest growth sector of medical research in Japan, making up 12% currently of medical research funding in the nation ($1.15 billion in funding per year). So sure, you can have some frauds and mistakes but that doesn't mean that the whole field or that all stem cell research in Japan is bogus.
It could be more likely to seem that way if the only information you have about Japanese stem cell research is e.g. the heavily publicized news stories abouyt Haruko Obokata from the Riken Center for Developmental Biology. But also note, that it was Riken
themselves who blew the whistle on that researcher's work being bogus. When the research facility themselves are the ones bringing up investigations as to whether their own researchers are committing fraud then it's actually more comforting: Riken didn't cover up the scandal in order to protect their funding. Note that Haruko Obokata was a "guest researcher" at a 100-year-old institute with over 3000 researchers. It's a little unfair to tarnish the entire field of Japanese stem cell research because of the fraudulent research of just one person. Note, that her Japanese PhD was in Engineering, and prior to the scandal she'd spent two years working in medical research at Harvard Medical School - it was clearly the fact that she worked at Harvard, under
American stem-cell researchers, which landed her the job at Riken.
Compare similar incidents such as the Schon Scandal, in which a German research was faking "breakthrough" semi-conductor research. And won some prestigious awards before anyone worked out he was faking the whole thing. We can ask if semi-conductors are such a valid field, since nobody picked up the fake science for so long. But we don't, because we aren't innately skeptical about semi-conductors. So there could be some bias against emergent fields here, where we highlight a few scandals as if they represent the field, in a way we don't do for fields we "accept".