A. What you'll have to do will depend in how finely you divide your population. E.g. recent african immigrant vs. Slave descended are quite different demographics with different life trajectories and you'll be able to tell one from another very easily. There will be huge political fights over these categories.
B. If you do hire based on population demographics then two things will happen: You'll get a bit more inefficient workplace due to unperforming workers. But more importantly, you'll be surrounding people with a bunch of Xers (whichever the underperfoming demographics is. Hillbillies? African Americans? Republicans? Left handed folk?) who are underperforming. This will cause a strong association in their mind that X=less capable. Xism will then increase.
The influx of women to my workplace really didn't help my colleague's sexism.
You think your employer shouldn't aim to be increase the diversity of your team because that'd make you racist?
This is exactly why you can't reasonably accept treating one group of people differently - it might be a lazy recruiter half-ass'ing their job, but it might also be actual real racism. There's no way to tell by looking. The outcome is the same.
If you're willing to give them a pass you might just be enabling a racist.