I think that's a reasonable principle to apply, but at least as stated by the Wiki article it refers to avoiding "attributing irrationality, logical fallacies or falsehoods to the others' statements, when a coherent, rational interpretation of the statements is available."
Now if law schools have a rational argument for why they still use grades to determine who gets into law school even though it has been shown that GPA has zero correlation with ability as a lawyer, and that its main effect is to keep black people out of law school, then I'd love to hear it. But note that they would need a rational reason for doing this, not just any reason.
...even though it has been shown that GPA has zero correlation with ability as a lawyer...
A charitable interpretation of the actions of law school admissions departments would simply be that they don't believe this "fact" (a citation for which is desperately needed).
Further, you are attributing anti-black racism to a group of people (law school admins/profs) who routinely engage in pro-black racism (see, e.g., Grutter v. Bollinger). It doesn't even make sense.
If you knew twice as much about the issue, do you think you'd be more or less charitable than you are today?