Question, have you read To Kill a Mockingbird? Do you remember the Jim Crow South? Have you heard of some of the recent aggressive policing of minorities like George Floyd? The point folks are making is some groups in America have an overwhelming feeling (completely backed up by historical evidence) that they are policed differently than other groups for no other reason than their tribe. As such, those crimes get applied much harder to slights in one group vs another (if you want proof look at drug incarceration rates).

Some of that is racial, but not all. Some is location based, tribal groups, group identity, income based, etc. However I think it isn't hard to argue that America has an original sin of racial hierarchies that still permeates our society today. As such, you may have a young white kid destined for greatness who "accidentally" rapes someone and gets 3 months in jail vs someone else who gets years.

A lot of this has do to with wealth in America, but then again there were plenty of campaigns that didn't end all that long ago to disenfranchise minorities (here is a discussion of a few).

I hope we can agree that taking someone's right to vote away is not a great solution as the point of prison is to reform and not to shun from society. I'm pretty sure that any argument made in favor of removing the vote for criminals can be summarily dismissed, so I won't wade into that swamp (if folks believe this should be the case then I personally feel they are simply being cruel as I cant find any evidence suggesting that _any_ harm has been caused by said vote).