In contrast, special-casing few disadvantaged students is a local decisions every school or university could make independently, and initially it was an easy sell - a tiny exception to help a fraction of people whom life treated particularly hard. Nobody intended for that to eventually apply to 1/3 of all students - but this is just the usual case of a dynamic system adjusting to compensate.
But putting aside standardized tests, in the context of this discussion about Stanford, I think these accommodations are being used for ordinary tests given for classes, so Stanford (or any other school) has full control to do whatever they want.
Taking what is currently scheduled as a three hour exam which many students already leave after 2, and for which some have accommodations allowing them 4 hours, and just setting aside up to five hours for it for everyone, likely makes the exam a fairer test of knowledge (as opposed to a test of exam skills and pressured time management) for everyone.
Once you’ve answered all the problems, or completed an essay, additional time isn’t going to make your answers any better. So you can just get up and leave when you’re done.
In real life, you're rarely given unlimited time for your tasks, and workers who can do more in less time are considered better than the ones who always need deadine extensions, so why not grade that too?
I'm also fine if a teacher or organization decides they just want to evaluate competency at the underlying material, in which case I think a very generous time limit should be given. Here the time limit is not meant to constrain the test taker, but is just an logistical artifact that eventually teachers and students need to go home. The test should be designed so that any competent taker can complete well in advance of the time limit.
I only object to conditionally caring about the thinking speed of students.
I didn't because I'd use the extra time to go over my answers again looking for errors.
It's that much harder to change the rules of standardized testing for all students, for complex and possibly dubious reasons, than it is to make an exception for small number of clearly disadvantaged students. One is inviting nation-wide political discussion on the merits and fairness and consequences of the changes, the other is an isolated act of charity with (initially) no impact on the larger educational system.