People have to be given a way to think about this that's compatible with their self-regard. Berating them won't encourage them to be more curious about what happened and why.
My guess is that the most effective way to make people think usefully about this would be to show users the IRA-sourced memes that they themselves shared or liked. When they log into their social media accounts, they should see it laid out in front of them.
It should be framed as an apology from the companies in question. "On Date X, we allowed this meme to circulate on Facebook. We now know it wasn't created by your friends, but by a hostile foreign intelligence agency."
Then people should *see* any memes they liked or shared that can clearly be sourced to the IRA. If people see it--without any kind of political message--they may be more likely to ask "why."
Seeing this should be prefatory to using their accounts again. Otherwise, I suspect berating, castigating, or intimating that voters are fools will only close their minds, resulting in total denial. Which isn't useful.
