Government IS the check on corporate power! You are the one who is misunderstood. As a libertarian, I believe governments are vital to a civil society (never said I was an anarchist). I believe governments SHOULD have (granted to it by the people who it represents) pretty ultimate powers in dealing with bad-actors. However, those powers should only be used in very specific situations; Does person A's actions infringe on person B's rights. Spewing toxic smoke into the air and making me sick is an act of physical violence towards me; the government should step in. The government picking winners and losers in a marketplace based on special interests and who can lobby more effectively doesn't protect my rights - it infringes on them.
All people, whether they work for a massive corporation or within the government, make most of their decisions based on personal self interest. Give corporate entities unfettered power, they will stomp on people. Give government unfettered power, they will stomp on people. It's all about channeling the individual's drive to improve their own life towards the best interest of the collective. A free-market and a government whose sole purpose it is to protect individual rights, is the best way to do it.
I don't believe in unlimited corporate power because people are fallible. I don't believe in unlimited government power because people are fallible.