There is tension between a hypothesized universal "right" of voting and the use of voting as a real-world method of choosing people to govern a country in a wise manner.
You see this tension when, for example, the ACLU advocates for restoring voting rights to violent felons. Personally I think violent felons have showed remarkably below-average decision making capabilities and I don't see why they should have a voice in running the country. However the ACLU seems to think that removing their voting rights is an affront to human dignity.
For many, democracy has become religion. It is no longer presented as a wise way to run a country. It is simply the unquestionable, universal, and only morally correct method of running a country. That's a dangerously inflexible stasis point for our thoughts to settle in, but that's where we are.
I prefer to avoid discussions that focus on the moral dimensions of voting. I would rather discuss how different government schemes are likely to effect society's well-being. I find these discussions to be much less predictable and more interesting.
Now, a voting test might be a good idea, and I would love to see it applied to adults too. Who knows, it might even elevate the level of political debate in this country to the point where candidates actually discuss substantive policy ideas. Of course, it would only last until an election cycle where women or a minority racial group had a lower than average pass rate, then it would be deemed "evil" and scrapped.
A disclaimer: I got halfway through and stopped when I ran into the giant pile of steaming kneejerk partisan assumptions (Oh look. A "George Bush is evil" quip. How original. Did it take a physicist to come up with that?). I'm bored and disgusted by this level of thinking, and I was somewhat surprised to see it from someone who argued so intelligently up to that point. So, if there is anything interesting after that segment, I missed it.