I don't know much about anti-trust laws in the U.S. But I can talk on behalf of the EU.
There are a lot of aspects to anti-trust laws. I guess it would be most fair to discuss each regulation separately. For example I think the exclusive dealer laws are total bullshit. Exclusive dealer laws basically means that it is illegal to make a contract stating that you will only use a specific company as supplier of a given product, for some given time.
This create some horrendous cases e.g. a case where a belgian couple who owned a bar, made a deal with a beer company who would install a beer tap for free and give discount on their beer, on the condition that only their beer could be sold on the tap. Then a third beer company who felt excluded, sued the couple and the beer company who installed the tap, the case was brought to EU, and the EU court of justice brought down the hammer with a huge fine.
Anti-trust laws are made in order to create a healthy and competitive market. But imo shit like the above does nothing else but hurt the market.
Then you have laws regulating price fixing, mergers, cartels, predatory pricing etc.
It's been some years since I have dealt with the subject. But during the time I did i reached the conclusion that ~80% of the laws were complete nonsense, when you looked at it with an economic lens.
You can probably find a lot of Friedman on the subject.
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The problem with monopolies is that they become so big and powerful that essentially they crush any potential entrants into their market. This can be done a few ways but the most common way is to drop prices for a sustained period and take a loss until your potential competitor goes bust.
They can also stifle innovation imo.
Yet this strategy of predatory pricing has never been observed with any concrete evidence behind it in reality. It's easy to see why. Try to think about how risky it would be to engage in it. There would have to be a high entry barrier to the market, otherwise it would be completely useless, that limits most markets. Then they would also need to have substantial financial reserves to keep it up. Complete insurance that no other competitor would jump in after they scare away the first one. Be ready for the much lower revenue stream. Ensure that the new competitor can't "tough it out" etc.
There really are a lot of things one could think of that could go horribly wrong with that tactic, and it's hard to see any scenario where a business would be so short sighted with their strategy in the face of competition.