If I remember back to my anarchist philosophy, that is ceding too much ground. Patents, access to cheap capital, "artificial" interest rates etc... are all government influence that large companies can take advantage of to become monopolistic. Without those the argument goes, that firms would never get so big because competition would sprout up immediately to cut into their market dominance.

If you look at Standard Oil or Bell System, the case studies for all monopolies, they all hinged on some government grated protection. In Bell's case it was initially a patent and then subsequently "legally sanctioned regulated monopoly." In the case of Standard Oil they utilized Trusts, which were legally recognized forms of distributing ownership to stay within the law.

So unfettered capitalism might not lead to long and enduring monopolies, but it would be much nastier and competition much more fierce because the systems on which business is built today would have to go away in total - to include regulated banking, infrastructure standards etc...

The question should instead be: Is the world in which there is no regulation one that you would actually want to live in? I would argue no.

edit: Note that I don't agree with this view, it is however the argument that is made.