Bain used leveraged buyouts. Bain literally borrowed money in the name of the companies they were taking over, driving them into debt. There is much research on Bain and others that shows this debt makes those companies unhealthy and more likely to go bankrupt. It’d be fine if Bain bought those companies with their own money, but they didn’t. Bain made sure they profited first whether or not those companies went bankrupt under the heavy debt load.
I’m not a Romney supporter, but what the hell else was Bain supposed to do other than to do their best to make sure they made money no matter what? Not that any company is able to actually do that all of the time, but they sure as heck don’t enter into an arrangement where chances are they will NOT make money. That would be stupid.