Here's the thing about leaving Japan: it's always way more dangerous than staying in Japan. US homicide rate is like 10x higher. I'd bet your "upstanding" friends have layers of reservations about visiting.
Popular culture likes to portray Japan as a weird outlier country- but that's only if you compare it to the US. If you include the aforementioned European countries in the comparison, the US is the weird country.
I have bit heard anything of the like in Japan, but as you say it could be because they don't have the same measures/report rate we have, or that I don't check Japanese statistics as much.