The threat to Europe has nothing to do with Russia.
Anyway, no one is saying disarm. The question is who pays for it. If Europe isn't willing to fund their own defense, why should we? Same with Japan and the rest of asia.
The other question is why are we obligating ourselves to go to war with Russia or China over countries that are not in our vital interests? Turkey's reckless shootdown of a Russian fighter could have resulted in us being obliged under Nato to go to their defense. Why would we let a repressive islamofacist dictator in Turkey drag us into war with a nuclear-armed russia? WW I and WW II were both arguably set in motion because small countries were emboldened by defense treaties with larger countries.
The US should use Japan as a bargaining chip. Plain and simple.