Prison is an unfortunate reality of civilization. As much as I adhere to a sense of idealism, crime is the product of the human condition, and until the end of civilization, crime will continue to occur within the borders of human society. The reasons behind crime are too numerous to count, but at the end of the day, criminals are still human—no matter their crime. 
With this being said, the function of a government is to make and enforce laws, and the enforcement part of that equation dictates that the government has to provide justice. For the vast majority of crimes, justice is doled out through separation from society. If you do not play by society’s rules, you do not get to play in society.
The traditional way of going about this separation is through the arm of the state. The state, which embodies the laws of society, is what incarcerates criminals, for the state is the appointed medium between the affronted and the affronter. In bygone ages, the state would be the sole operator of both courts and prisons, for again, the state has a vested interest in maintaining the rule of law. However, this has changed. 
The advent of private prisons has allowed the profit motive to enter the system, and this entrance precipitates further ethical concerns about America’s criminal justice system. To understand this introduction, it is important to understand the context of its beginnings.
As reported by The Sentencing Project’s 2016 report on correctional trends, the U.S. prison population is currently around 2.2 million people, which is a 500% increase in the last 40 years. This is an extreme drain on public funds, and as a cost-saving measure, the 1980s saw the beginnings of private prisons used as a hopefully cheaper alternative. 
Now, it is also important to understand private prisons are not the root cause of mass incarceration, and the Prison Policy Institute’s 2019 report by Wendy Sawyer and Peter Wagner shows less than 8% of the U.S. prison population is in a purely private prison.
However, here is where the ethical concerns come in. Private prisons are for-profit. “Obviously,” one might say, but consider both the product gaining profit for private prisons and the inherent nature of capitalism. 
Capitalism is predicated on the idea of growth, and there is no end point to the market. The market just is.
What private prisons bring to said market is the product of incarceration. They provide the service of detaining people for a determined amount of time, and they are paid for their service, like any other for-profit business. Private prisons are incentivized to grow, as is the purpose of a business.
How does a prison grow? They have the options of cutting costs for more profit from their revenue, getting more prisoners to make more revenue, or both. The obvious and disgustingly practical answer is both.  
Lobbying for policies which create more prisoners is one major way. Dean DeChiaro of RollCall reported GEO Group, a private prison contractor which frequently deals with Immigration Control and Enforcement, spent $1.3 million in congressional lobbying from Jan. 1, 2017, through Sept. 30 of the same year. Coincidentally, ICE was proposing five new immigration detention centers around the same time. There can be no definitive lines drawn here, but I am hoping I have at least sketched a picture.
As for cutting costs, the results of a 2016 Justice Department report on contract prisons, privately-owned and operated, reveal the end result. Contract prisons had higher rates of safety or security incidents per capita than public prisons, and in one instance, a monitored contract prison failed to discipline 50% of those incidents.
Private prisons had more contraband confiscations and assaults, both inmate-on-inmate and inmate-on-staff, and two of the three contract prisons which were singled out for deficiencies by the Bureau of Prisons had been improperly placing prisoners in Special Housing Units, which are usually reserved for disciplinary or administrative segregation until more room was made in the general population.
Cutting costs leads to improper management and worse conditions for both prisoners, which I will remind you are still human, and staff. 
Contract prisons were almost discontinued in 2016 by the former President Barack Obama administration, partly due to the 2016 report by the Justice Department, but former Attorney General Jeff Sessions rescinded the directive in early 2017.
I posit the issue is worthy of continued protest, however. The well-being of people, criminal or otherwise, should not be dictated by the profit motive and board members. Public prisons have many issues, some of them similar to private prisons, and mass incarceration will not be fixed by the abolition of for-profit prisons.
Regardless, the abolition of private prisons will bring the well-being of prisoners under the sole directive of institutions beholden to the people, and it will be our job to further fix the mess our country has made with so many lives.