That's a devious analogy. Racism is not the same as acknowledging genetic differences. If people with darker skin are more likely to suffer from D vitamin deficiency, wouldn't we want to be informed about it? Reversely, should pale people simply ignore being burned by the sun when visiting tropical places?
Yes, but go back to the topic, to carry on with the idea of "physiognomy to defeat injustice". Blood type C correlates with increased shoplifting: then what? You study the matter further (good)? Or you approach Roger Slackermeyer strong of a 90% confidence of something (well...)?
> Blood type C correlates with increased shoplifting: then what?
Then you take appropriate measures, or you don't. Compare it to regular diseases. If you have a history of cancer in your family, you would probably want to go on regular screenings. Or if your family has a history of suicide, perhaps you want to pay special attention when your kids are feeling depressed.
So, consequently, prejudice is something that must be absolutely discouraged. In fact, you mentioned «injustice» as something to be «defeat[ed]», and that an individual can be subject to prejudice (owing to similarities to others) is radically unjust.
Edit: make the intellectual experiment, put yourself in those shoes and run the narration. It's you who has "that" trait. The law enforcement treats you differently. The HR treats you differently. The neighbourhood treats you differently. But you have your individual traits, not the virtual ones. Now put yourself in the other side: there is a trait for the median, and there is an individual there: how much should they rely on the trait of the median? Veeery relatively, and with all alert against pitfalls of bias, would not you say.