"Democracy is based on the assumption that a million men are wiser than one man. How's that again? I missed something. Autocracy is based on the assumption that one man is wiser than a million men. Let's play that over again too. Who decides?"In Robert Harris's novel "Archangel", I recall a scene after the death of Stalin where the secret police chief, Beria, tries to manipulate his colleagues to ensure his own succession. He has a cunning plan but it does not end well.
A politburo colleague observes that Beria, like many very smart people, assumes that more average people will never figure out what he's up to. But that's to mistake the nature of average folk: it's not that they can't get there - they can; it just takes them a little longer.
That's why I'm not that worried by the left-hand side of the bell-curve getting the vote.
The not-so-super-smart are usually not au fait with the niceties of public policy options, but they tend to be pretty expert on whether things are working out well for themselves. And in the end, that's a recipe for a stable and productive society: keep the punters reasonably content.
If you disenfranchise swathes of the population, you reserve political power to the vested interests of those who retain the vote. Naturally public policy will be captured (in the economics sense of regulatory capture) by such vested interests.
In the long run, this is seldom a good thing.
Sentimental, moralistic platitudes about the 'ethical superiority of democracy' don't do it for me.
No, I'm strictly functionalist. Democracy should be supported because it's the only system which provides a regular and universal protocol to "kick the bastards out".
Note: if you want Robert Heinlein's considered view as to how to make democracy work, you should read "Starship Troopers".
Tl; dr - voting should be restricted to those prepared to defend society, so no votes for parasites. Basically you do your military service, indicate your willingness to put your life on the line for your country .. and then you get to vote.