That is not really an alternative explanation as much as it is an additional explanation. The political motive (the votes) does not contradict the financial motive, the go together like peanut butter and chocolate.
Not that I agree with the idea that it is slavery, calling it that diminishes the horror that is slavery. But I do believe there is a powerful profit motive involved here, and keeping people locked up so you can make more money is evil.
If you claim that private prisons steer public
policy to increase incarceration, where's your
evidence?
I know of isolated cases, but you're claiming
a nationwide conspiracy. You're in effect claiming
that where there's a motive there's a crime, even
if you've not demonstrated the crime.
If the mere existence of profit, ie, financial gain,
is proof of undue influence / a conspiracy that
affects the entire justice system, then this
rationale has broader applications. Any group
who'd benefit from prisons would be causing
mass incarceration, eg, prison guard unions,
municipalities with prisons. This would apply
to both government
and private prisons.