The Fed DOJ's antitrust division--the primary antitrust enforcement arm--brings antitrust lawsuits when it believes that a company has too much market power. In short, a business without much market power can perform "anticompetitive" acts (you may only buy my widget if you also buy my thingy), but a business with lots of market power cannot (I am the world's preeminent widget supplier, so I cannot force you to buy my thingy along with my widget).
For the first 80 or so years of the Sherman Antitrust Act (and the associated antitrust laws that followed), the antitrust division relied heavily on how many actors existed in a market to determine whether to challenge a merger or bring an antitrust lawsuit. Example: there are only 8 companies that sell a widget in this geographic area, so my company cannot (a) merge with one of the other 7, or (b) perform some anticompetitive act (forcing my customers to also buy thingies from me).
In the 1980s, the antitrust division adopted the "Chicago School" view of market power, which changed the calculus from how many competitors there were to how much ability does any one company have to impact the market price of an item. This was a big deal because instead of protecting the other 7 widget suppliers, the antitrust division essentially said that as long as there is still significant price competition for a widget, you can do what you want regarding the sale of thingies, and your widget suppliers can merge to your heart's content. As long as there are two or three widget competitors who are big enough, I won't be able to control the price of widgets myself. Many people argue--and I'm not well enough versed to know--that this resulted in the collapse of "Main Street" businesses, leading to consolidation and oligopolies.
None of that is price controlling; the theory is that as long as there is robust price competition, prices will remain low. So Lowes and Home Depot have cornered most of the traditional hardware store market in many places, running all of the small hardware stores out of business, but because prices are still low, DOJ approves. (That's simplistic, but demonstrative.) Markets are still subject to price fixing (another big no no), which raises prices, but is rare in the traditional sense of all four remaining widget suppliers getting together and agreeing what to charge for a widget.
However, in an oligopoly, conscious parallelism--realizing that your competitors are setting a higher price that all of you widget suppliers think the market will bear, and setting your price to match--is easier to pull off, and similarly results in higher prices. Because there is no "agreement," there is no antitrust violation. Gasoline and airline prices are good examples of this in action. The fewer the market participants, the easier conscious parallelism is.
So what am I saying. Not entirely sure--basically spewing random stuff on a message board, but maybe:
When people talk about gouging, they are basically talking about whether companies are taking advantage of too much market power, essentially antitrust concerns. Pricing for what the market will bear--CAPITALISM (writ large)--is not gouging, as long as there is true market price competition. However, in markets that are closer to oligopolies, conscious parallelism starts to look a lot like gouging, but isn't considered an antitrust violation because it doesn't require actual agreement. AND under the old fashioned way of looking at market competition (how many competitors are there), maybe it would have been harder to do.