Policymakers are constantly having to choose between policies that benefit one group and hurt another group. Whether they're deciding whether or not to put a new on ramp in on a highway or how to structure tax policy, no matter what they do, they're going to hurt some people and help other people.
In a democracy, you're not elected based on how much benefit you create vs. how much harm you create, you're elected based on how many people got more benefit than harm. So, politicians are better off imposing 50 units of harm on 1 person and 1 unit of benefit on each of 9 people than they are imposing 1 unit of harm on all 10 people. In the first scenario, 90% of the voters think you did a good job and in the second scenario, 0% think you did a good job, even though the second policy is actually much better overall. So, they have a huge incentive to spread benefit widely and concentrate harm narrowly.
When the policymakers can also disenfranchise voters, then that whole calculus is even uglier. Then they can pick one community to always dump the harm on and then rig things so that a large percentage of the people in that community get disenfranchised to further minimize the electoral fallout from the harm.
So, what would be the optimal strategy? You would want to pick a community to serve as your dumping ground. Whenever you have the choice about what community gets the halfway house, the airport flight path, the sewage treatment plant, the worst teachers, etc., you pick that community. Whenever you have a choice about what community gets the new science lab in the school, the small business loans, the light rail station, etc., you pick other communities. That way, you're able to give the other communities fewer problems and more benefit than you would be able to with a more equitable distribution of harms and benefits, so they vote for you while by stacking up the harms on as few people as possible, you only lose a small number of votes. You want your dumping ground community to be as insular as possible so that the friends, co-workers and family members of the people there are all contained, so you build highways encircling it, you cut off public transportation to the dumping ground and you undermine social mobility so nobody can get out. Then, you make as many crimes that come with the poverty you're creating into felonies as you can. You crank up drug offense penalties, you make multiple petty misdemeanors into a "three strikes" felony, etc. And, you flood your dumping ground with cops to try to convict as many people in the dumping ground of felonies as possible to diminish the electoral impact of that community as much as possible.
That all may be an overly diabolical description of what policy makers are thinking. In reality, most of them mean well and many wouldn't ever consciously do any of the above. But, it is hard not to notice that the things above are exactly what the policy makers do in fact do. It isn't that individual policy makers hatch this evil plan, it is that each individual policy maker responds to the same incentives without ever really being aware of the big picture. They just know that when the bus breaks down in the rich part of town, they get more calls from city council people than when it breaks down in the poor part of town, so they eventually find themselves assigning the new busses to the rich part of town in order to avoid getting hassled. Politicians who favor tougher criminal penalties for the people living in the dumping zone, who may not be thinking about this whole scheme at all, just nonetheless win more elections because the system is rigged to favor politicians who adopt the strategy above even if they aren't doing it on purpose, so the strategy stays in place.
It isn't just about felon disenfranchisement. The incentive to concentrate harm in as few communities as possible exists either way. But disenfranchising felons entrenches the problem and makes it even tougher for anybody who wants to fix the problem to win public office. Our entire Constitution is largely designed to protect the minority precisely to prevent this kind of harm dumping. Felon disenfranchisement drastically undercuts those protections by removing many of the people that get dumped on from the Constitutional political process entirely.
It is hard to see a path to state and local government turning this around. The political voice of the communities that are suffering from this problem has already been so muted by disenfranchisement that it is hard to envision their interests suddenly taking center stage. In some communities- whether defined geographically or racially or both- the level of disenfranchisement is completely out of control. There are neighborhoods in many of our major cities where more than half of the men have lost the right to vote. In the entire state of Alabama, 34% of black men lack the right to vote. No party is going to win enough votes in a state legislature to tackle a problem that primarily affects a minority group that only gets 3/4 of the votes it should. The protection of minorities has always been a central role of the federal government and I think we're at a point where federal action is the only realistic way out of the spiral on this issue.