The article linked was very interesting and got me thinking about "natural monopolies" being beneficial for capital accumulation.
I think it is all a mater of perspective and in the end it all comes down to a single moral principle: don't initiate force against others. Thus free competition will result in natural monopolies which allow capital accumulation and that is just the nature of good competition. Unnatural monopolies are the ones that are dangerous (such as those granted to patent / copyright holders) or via regulation. Anti-trust laws are also a major problem.