Quick note about the spelling thing - I agree on the whole, but you should be aware that there are glaring exceptions. Right now I work a lot with architects, for example, and many of them are very smart and yet have disastrous spelling abilities.
Since I observed that there are smart people who can't spell, I've revised spelling ability down to "weak indicator" of stupidity or poor education. I.e., if someone spells poorly and has a few other things going against them, then the spelling will help decide the matter. But I would not make any rapid judgements on someone's intelligence based purely on their spelling/grammar.
When it comes to taking tests, 99% of the population seems to me like they have serious brain problems. They perform far below my level, which I arbitrarily designate as normal. The kinds of "real brain problems that need some intervention" that we're talking about here are defined pretty empirically; we mostly aren't talking about things that show up on an MRI, we're talking about things that are "diagnosed" by people scoring 1½σ below the mean on an IQ test.
To take a concrete and fairly extreme example, I don't know what the fuck is wrong with people that they can see a word spelled correctly dozens or hundreds of times and still not know how to spell it. But that seems to be the case for 99% of the population.
The function of correct spelling in modern society seems to me to be essentially the same as the function of good penmanship a century ago: to demonstrate to the reader that the writer is properly educated, i.e. approximately that their parents were rich enough that they didn't have to pull them out of school in 1950 when they were 10 to work on the farm. Fundamentally, this is harmful to the social fabric. Either prejudice distracts from the quality of the writing — there are any number of Nobel-winning writers with terrible spelling and penmanship.
(I was expelled from eighth grade for picking a particularly inopportune time to explain this point of view, somewhat less articulately: coming in second in the regional spelling bee, if I remember correctly.)
It's fortunate that this particular neurological deficit doesn't happen to cause any harm, and unfortunate that we choose to stigmatize the 99% of the population who's dramatically worse at it than I am. But given that there's a relatively safe drug that allows many people to escape that stigma, it seems reasonable to let them have it until such time as we can expiate the stigma.