As for society collapsing, I think you grossly underestimate the value low intelligence people can provide when suitably directed. Consider walmart - it's a vast command economy which employs about 1% of the US (mostly taken from the bottom percentiles) and has improved the standard of living for millions.
A bunch of morons couldn't create walmart themselves. But they can still create great value when directed by a small number of intelligent people.
we'd just bar morons from voting.
This lead not only to a total political gridlock for years, but to actual death and mayhem.
You can't have a semi democracy where the elite decides, who's eligible to vote. It's either all or nothing.
The problem with the term "moron" is that it is too easily applied to mean, "people who I don't think should be allowed to vote, no matter how intelligent they might actually be."
The fact that racists favor a corrupted version of a certain policy does not imply that the policy is bad.
Historically, that's just an oligarchy or plutocracy.
Heck even being governed by a "council of elders" is a semi-democracy if not all elders are approved by the council to join their ranks.
A standardized test would be hard to impose, since how does one measure someone's ability to make good judgments about something?
Then, the next step would be preventing them from having kids...
You know it's a very, very bad idea. Morons are part of the society and deserve to have their voices heard. Any democratically elected government mirrors the society it came from.
If people can only read well enough to be consumers but not producers then it's only so long before society collapses, regardless of whether or not they're getting their vitamins.