I don't trust the government to do much of anything, and that includes invest money. Their stewardship of the social security trust fund has proven that I'm right (it's essentially full of IOU's). Anybody who believes that giving the government a few thousand dollars is better for their retirement than putting the same cash in a 401k hasn't taken a hard look at the government's performance to date.

TL;DL: I don't think that argument would fly with informed voters.