Easy solution: Prosecute all criminals, investigate all crimes.

And recognize that it's still a filthy gaijin doing it, and better immigration controls and screening could have prevented this. It wasn't "Takada Ryusei, born in Kyoto, to parents born in Narata, to parents born in Hiroshima" doing this crime.

This loser is likely on a tourist visa, which have much more lenient screening, but maybe it should still have a step or two of "a quick glance at your public-facing social media for blatant Antifa-posting".

The stiffening of tourism borders would sadden me, as a person who enjoys tourism, but it would be entirely understandable, and I'm willing to jump through a few hoops if it means the places I visit will indeed be places I visit, instead of just "back home, but with a different longitude and latitude".