Also
>evil foreign criminals
Like who?
It's a problem for their soft power because it means they can't do any of the cool music genres. How can you have metal bands or rappers if none of them are allowed to do drugs or commit any crimes?
(If there's a hint any musician knows what a marijuana leaf might look like they and all their work get instantly deleted entirely from society. Although they do let music producers sexually abuse all the talents they can get their hands on.)
Drugs and crime aren't really in the metal imagery, I'm not convinced it's the explanation (also I don't think metal culture has ever really been significant soft power, always been too niche)
Oh no I had a list of good Japanese rock, metal and rap music right here but I seem to have dropped it...
Hanabie: https://www.youtube.com/watch?v=fuFbQ-Mewfw
Mad Capsule Markets: https://www.youtube.com/watch?v=Al1ihLf_e18
Maximum the Hormone: https://www.youtube.com/watch?v=beN5ep5MrdY
Jiluka: https://www.youtube.com/watch?v=psEMRalCPFQ
Deviloof: https://www.youtube.com/watch?v=LWDENni6Pbc
Nemophila: https://www.youtube.com/watch?v=26aMuahxz8c
Unlucky Morpheus: https://www.youtube.com/watch?v=V8i_QhOgsKw
Ningen Isu: https://www.youtube.com/watch?v=CbI79e5iZKs
Band Maid: https://www.youtube.com/watch?v=MZIJ2vFxu9Y
Stereopony: https://www.youtube.com/watch?v=vYV-XJdzupY
Gallhammer: https://www.youtube.com/watch?v=eDiWv276t78
Chanmina: https://www.youtube.com/watch?v=efcyoenRdnE
Wednesday Campanella: https://www.youtube.com/watch?v=A1oxh8Z-2ko
Tokyo Gegegay: https://www.youtube.com/watch?v=A9W6rvoqIME
Can't have sex, drugs, and rock-n-roll, but you can still have two of three.
Japan has rock. The have punk. They have metal. They have rap. They have deathcore. Go through the list. Look up fucking Hanatarash. Take ten minutes to Google. They have everything.
You don't need "sex drugs and rock and roll," you just need an appreciation for the culture and a sense of alienation and rage against an oppressive system. Which, despite your belief that Japanese people cannot even comprehend the concept of illegal activity or rebellion, they do have. You need to stop looking at people and cultures in terms of reductionist stereotypes.
Maybe legalization would be better for society, though who's going to reap the profits appears to be the main driving factor.