It should be though. Unchecked monopolies, duopolies and oligopolies are antithetical to a free market economy - they stifle competition and make the market un-free as well:

- for employees, they're bad because monopolies (or cartels) suppress their freedom to go to a better employer. The best case to look at is actually the tech sector, where large corporations colluded to keep compensation down [1], but there's also more evil cases like WalMart that go as far as underpay their employees so badly that they can only survive on food stamps [6].

- for suppliers, they're bad (in the correct term of a monopsony) because having only a few (or only one) buyer depresses their ability to get fair prices for products, e.g. in agriculture [2], or in WalMart [3][4]

- for customers, they're bad because they can't (realistically) go to alternatives, especially if the monopoly in question has extinguished competitors by advantages of scale - again, WalMart is a nasty example [5].

- for society as a whole, they're bad because, again, large actors like WalMart can devastate vibrant community centers like malls, leading to dereliction of entire neighborhoods in a domino effect [7], and eventually the erosion of local tax bases, leading to funding issues for basic government services.

[1] https://en.wikipedia.org/wiki/High-Tech_Employee_Antitrust_L...

[2] https://usceconreview.com/2022/07/06/america-where-even-sust...

[3] https://www.businessinsider.com/wal-marts-suppliers-feel-pre...

[4] https://www.wsj.com/articles/wal-mart-ratchets-up-pressure-o...

[5] https://www.investopedia.com/terms/w/walmart-effect.asp

[6] https://www.cnbc.com/2020/11/19/walmart-and-mcdonalds-among-...

[7] https://www.cnbc.com/2020/06/20/how-mall-closings-in-america...