I can see how what you're saying could make sense, from a utilitarian perspective. But unfortunately lifetimes of empirical evidence suggest that we just can't trust any of these industries (oil/gas/mining, banking, pharma, telecom, etc) to self-regulate (which in effect is what the "revolving-door" culture leads to).
Not all of the people in these companies are bad (most are not). But enough of them are, and the temptation for malfeasance (both to maximize profit, or to simply save their asses when the inevitably run into hot water), along with the human tendency to rationalize away such malfeasance (if it serves a perceived higher end) are simply too great.