Meanwhile, in a less politically charged situation, it's pretty normal, or at least smart, to go back over any area where you messed up with a fine-toothed comb.
If, and this is a rather pessimistic assumption, if the student is likely to lower their grade on a re-test, in my experience it's more likely to be because the original grader was being generous in the face of ambiguity, rather than systemic random errors. That's because the graders are mostly nice people. If that's not good enough for someone, they damn well better have a good reason for it. I have no problem with policy that enforces this. The politics are a distraction from the ethical question.
That's not the same thing as the original, which implied "my grading is so random, hope you're lucky on the rescore".
Edit: I had a high school teacher with a policy where she’d add X points to every score from the get go, and you’dlose those if you objected to grading, so you’d only object for misgrades by more than X. But that’s not the same as the original “okay, let’s roll my truth-recognizer dice again!”
It reminds me of those "drunk driving costs you $15k" ads, where most of that comes from the expense of navigating the court system (bail, attorney's fees), and the state is somehow proud of this fact.
It is the professor's responsibility to grade accurately, and honestly if there is so much inconsistency in grading that there's a significant probability that the student will lose marks despite having pointed out a reason they should gain marks, the professor is screwing up very badly[1]. Don't pin that on the student not having noble intentions or whatever.
[1]:Or at least that's the case in STEM. My humanities friends tell me that grading is much more subjective there which is a bit disturbing but I'm hardly qualified to make such judgments.