You missed the part where the JCP tried to start a Protracted People's War on Stalin's orders, but the completely war-weary Japanese population totally rejected them and they ended up just giving the occupiers an excuse to crack down on themselves. Basically every leftist in Japan was considered a terrorist by the average person until the 80s when enough time had passed that they could rebrand as pacifists, but by that point the political machine of the Liberal Democrats had become all-encompassing.