Because government is the only thing big enough to combat these trusts/monopolies. Especially when they are an important or essential service.
Except, you know, the Market.
An incumbent naturally has an advantage and when someone new enters the market the incumbent uses their advantage or their larger capital to crush or assimilate the competition. Not always, but I can happen.
Of course the larger, already used company has the advantage, that's how it'll always be, that's how economics works. What are we supposed to do, go out of our way to give every start-up that's offering inferior products business? No, that's ridiculous.
Is this fair? Is this okay? Does this have a negative impact on the market and on the consumer? The federal government thought so, and stepped in.
No, yes, and yes. Also, the Markets also thought so, and thus, Linux and iOS were born (amongst other, smaller ones).
Yes, and as you mentioned, competition lowers prices and improves services. In every single market.
Should the shale producers run dry and we go back to one provider for oil, are you okay with them bending over their market and raping it in the ass because there is no competitor?
I'm absolutely okay with it, because that's their right, as the sole producer. If the consumers want the product, then they'll pay for it. If not, they won't. And that's why we rely on things like renewable energies to pick up the slack, and keep them in-line (now, that is, not 20+ years ago). Were the Shale to run dry, or be forced out of business, of course prices will go back up, to cover their lower profits/losses recently. That's their job, that's the job of every company in the world, who are we to tell them not to try and make as much money for their shareholders as possible?
your example is proof of why someone or something has to monitor the market to stop monopolies. And it just so happens that the only thing big enough with enough power to do that, is government.
Again, I disagree. Without government involvement in business aspects, the Market would be free to offer viable alternatives to whatever monopolies spring up. For instance, it's government that's allowed Comcast, TWC, and others to gain Trusts on the cable/ISP markets, refusing individuals, start-ups, and towns/cities to start their own ISP's, networks, and companies. Without gov't involvement at the State and Federal levels, we'd have much, much more competition in the marketplace. Instead, people (especially in the Reddit Hivemind) have been looking to the FCC and other gov't entities to regulate the ISP market more, as if more government intervention will somehow help. I, for one, strongly disagree.