Fujimori is hardly the best example when considering dual nationality.
The people I know are older than 22 and didn't make a choice. They are Japanese in Japan (and at their embassies) and are Japanese and English (or American) outside of these realms.
My husband returned to Japan for similar reasons to you but needed to stay there as those circumstances were ongoing. Although he had been in Britain for long enough to be offered citizenship, once he had been in in Japan for a few years he was no longer able to return on anything except a visitors visa. As someone who was schooled in Britain, who speaks English as his first language and who is more or less illiterate in Japanese, this would hardly seem fair either. But that was his choice.
The law changed in the UK too, From the early 80s onwards we found that my mother (who never took up British citizenship - and never will) would have lost any right to live in the UK had my Father died. Now that the UK & Spain are both in the EEC this has probably changed, but this was a serious threat to my family when my brother and I were going through School.
All countries have dreadful policies. I'm not sure it's right to say any are worse or more xenophobic than others. They're all appalling when you find yourself on the wrong side of them.