in a market the search for profit is the search for more efficiently serving aggregate preferences of consumers. allowing corporations to assume disproportionate control of the political process is almost assuredly a net improvement.
Here's Cato's take on anti-trust: http://www.cato.org/pubs/handbook/hb105-39.html
Besides, I don't agree with you, because it doesn't take into account externalities. When "efficiency" takes the form of polluting the river because someone else will clean it up, it most assuredly is not a net improvement.