I'm afraid your understanding of how businesses and equity markets operate and, even of some basic economic facts, is very seriously deficient.
The companies that are targets of Bain investments usually are already saddled with nore debt than they can repay, and have zero ability, on their own, to acquire more debt. Bankers, to use a common phrase, lend money only to businesses that can prove they don't need it. Existing debt must be repaid and the company's performance restored, in the restructuring by Bain, BEFORE any new debt can be taken on. Bain has to prove, to very skeptical banks, that the restructured company can, with a very high confidence, repay the new debt it is taking on - and their starting estimate is usually not good. (There are no government insured or mandated loans in the business market as there are in that for housing: it is a hard-nosed process.)
Bain specializes in the creation of specific investment funds for such turnaround aquisitions. i.e. they announce their intent and join with other investors to create the investment group that, under Bain leadership, does the aquisition and turnaround.
Bain then buys all or a controlling interest in the target company using its capital (i.e. money) and that of other investors in its team. Thus the new team has a serious stake in the game. If their effort fails, they stand to lose all or most of their investment in a controlling stake in the company.
Your blythe accusations of "management" notwithstanding, the existing management of the target company is usually tossed out after the change of control, and a new one specified by the new owners is installed. It's true that Bain often installs members of its own team, well-experienced in these restructurings, in the new management. However this is no different than seeking a well-qualified and expert surgeon to perform a difficult and unusual operation on a seriously injured patient. (It appears to me that you imagine that managing a company is an easy thing, requiring no skills or experience.)
Following the turnaround, the successfully restructured company is again sold to other investors. They are generally not fools and are willing to pay only a price based on the reasonable expectations of the future returns of the restructured company. If most of Bain's restructurings didn't work (as you imply), that would be very quickly reflected in the future resale value of all the restructured companies it sells. In such a case Bain would be unable to attract investment partners to begin with. In particular, if it looks to proficient and seasoned investors, that the restructured company in question will still fail, then the resale will surely not recover the Bain investment. All of this contradicts the unproven assumptions on which your wildly inaccurate diatribe is based. It is a market-based effort to salvage value (and jobs) in failing companies. Like any business it involves risk of failure, and it is not successful 100% of the time, but it is a market-driven process all the way.
In all of this , you are here merely reciting highly distorted and deceptively assembled snippets of disjoint, mutually inconsistent, facts extracted from a large body of such investments and turnarounds, some of which lose money foe Bain and its partners - and all of which ignore the central tendency of Bain investments. There are two possible explanations for this;
1. You are merely reciting propaganda you have read in the blogs and progressive opinion pieces you frequent, and lack either the knowledge & understanding (or perhaps just the inclination) to detect the many obvuious distortions of truth in them.
2. You do understand, but are lying for purposes of argument.
In either event you very much appear to lack a basic understanding of how equity markets work. No transactions, neither sales nor loans, can be done unilaterally. There is always a partner in every transaction, the buyers and lenders, in the cases at hand, are also seasoned and experienced at what they do. Bain or any other like firm can't simply add debt to a company or sell it without the willing consent and participation of their opposite numbers whose motives, like Bain's, are to make a profit on the deal. The systematic deceptions you postulate (but for which you offer no concrete evidence at all) simply aren't possible. One may get away with that (to a small degree) once or twice, but once the pattern is seen the market will adjust.