I think that, the problem with "I told you so" is that it's revealing schadenfreude -- taking pleasure in the other's humiliation.
If you're trying to bring people to our side, then revealing such schadenfreude would be unproductive. People invariably feel all kinds of conflicting feelings as they become cognizant of the reality of the social structures and processes around them: despair, anger, frustration, and very little hope. In that fragile psychological state -- you are a fan of psychotherapy so you know what I mean, ya? -- I think it would push the person to, not embrace those difficult feelings and emotions but to, rather, push them away and become resolute in the position.
Schadenfreude directed at people who will _never_ come 'round? Who gives a rat's ass, I say.
OTOH, maybe people are just so fucked up, they want to be punished? And the "I told you so" approach would work? There's a segment out there that seems to want to be so punished, as Anatasia, the BDSM sex worker from BAD, used to tell us. But, do we want so many people who want to be punished on our side? That whole "I want to be punished" thing drives the hairshirt leftism that people often deride, no?
I dunno. It's a tough one. I guess you could say that the left might provide an outlet for people who are coming around to punish someone, punish the people to whom we are really directing the "I told you so" message. Is that what you mean?
In other words, by becoming the symbolic finger wagging at the evildoers, we give people a morality play to watch and identify with. They want to direct their anger at something, so we help them by chanting "I told you so" at Bushetal?
I can see that. Well, as usuall, I fumble around and don't know WHAT the hell I'm saying. At any rate, I have to get cracking so's I'll have time to transcribe. Not my forte Ben, but dang, I'll give it a shot! :)
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"Finish your beer. There are sober kids in India."
-- rwmartin