Pure capitalism is letting the market decide which leads to the monopolization of industries.
Nobody's ever succeeded in establishing a coercive monopoly without government backing. In a free market, monopoly is a non-issue. For example, when Alcoa was the only vendor of Aluminum in the United States, the pricing of aluminum fell continuously.
The first one is just a matter of "are you big enough, ruthless enough and no rules stop you, you can get rid of competition that way".
The second one - Bell - is interesting. For some services, like telephony, if you don't have government regulation you will get a natural monopoly. The phone companies would earn more money if they merged - no need to ever compete on price, or duplicate infrastructure. The price would be based on the value to consumers, not on the marginal cost of providing it as in a perfect market. And competition would be hard to come by - refuse to receive and make calls to this network. Knowing this, a competetive network would never appear in the first place.