You said — “It’s possible, maybe likely, that’s what he meant by the 88. It doesn’t mean he had any contact with neo-nazis or neo-nazi groups. Antisocial people take on antisocial trappings — nazi or satanist or vodun or radical Muslim. I wouldn’t read too much into it.”
No, I don’t think he was a member of any of these groups. I just think he took and borrowed from wherever he could find something, to construct for himself, in his imaginary world, a “case” for redressing the wrongs that he perceived had been done to him and to justify the action that he knew he was going to do — which was to kill all those students...
My interpretation is a little different -- he wasn't looking to radical ideologies for justification, but as a means to stir up more outrage. Like the scene in "Dog Day Afternoon" where Pacino stirs up the crowd by chanting "ATTICA! ATTICA!" over a botched bank heist that had nothing to do with the prison revolt.
It's PR, not justification. Cho, in his sick little mind, already had all the justification he needed.