Collusion and Monopolies happen all the time. The number one defender of Collusion and Monopolies seem to be mos tLibertarians.
If you're interested in reading more on the topic, search for keywords: rothbard, myth of natural monopoly
It is my experiences with defenders of monopolies. In my conversations with dozens of Libertarians they do not agree with me that the government should limit monopolies. I have a strong academic background and find that the philosophy of Libertarians is FAR from the grass root Libertarians' beliefs.
To illustrate, imagine we were in a free market and I wanted to start an oil company to disrupt the prices of an oil cartel. How am I going to do that if I don't have any oil?
By offering those resources to the same spaces that utilize oil, you are competing with oil. If you are able to take customers from oil, oil will be forced to reduce their prices.
As I mentioned in the previous comment, you should check out the keywords I mentioned. And if you are thinking that I'm missing something, please direct some resources my way.