codexerrata

An ad hoc test for certain jobs is certainly better in many cases, but they're not mutually exclusive. 

The same applies to measuring conscientiousness. Past work is preferable, but then again we do look at past work today. Grades will not matter much to many employers if you've been in the workforce for a decade. They may look at them, but they're only another data point -- I don't see how more data would be bad in this scenario. 

The rationale behind prohibiting questions of one's sexuality, I presume, is that sexuality is neither relevant for (almost) any job nor indicative of a relevant skill. 

The same definitely can't be said for the SAT, or really even for your history grade. A good history grade implies a certain level of literacy, the ability to turn in things on time, not sleeping with the teacher's wife, etc. You can of course make every applicant take an IQ test, but that takes time, and it's impossible to test an applicants long term conscientiousness. 

Of course, this also applies to asking about college degrees, but perhaps saving a large cohort of the population three years and a six figure sum is worth more than having the college degree as a proxy for conscientiousness and intelligence. 

Though I do not believe it is possible to prohibit the question, unless you also prohibit questions about previous jobs, prison time, time spent out of the country, etc.