Le Blue Dude, If you know some libertarians, then you've probably already heard many of our arguments, but just in case...
The thing about corporations is that they are a privileged type of organization created by government, not by the marketplace. It's debatable whether or not corps or something like them could exist in a free market, but without government, they wouldn't have any special privileges or advantages over other types of business even if they did exist.
More importantly is the current "crony capitalist" setup, and the incestuous relationship between government and corporations. For one thing, how much of the bad stuff that corps do is actually against the law? Not too much, really. But it's not just a matter of government being incompetent or turning a blind eye to corporate activities as it is that government, as a power structure, is more greatly influenced and corrupted by corporations than by its citizens. And government is not really likely to do a better job at regulating corps because of that. In short, much of the corporate power and privilege comes from government itself, and corporations would be less powerful without government to back them up, not more powerful. Without government, corporations can only stay in business the same way any business does, by attracting and keeping customers. No customers, no business.