For those who don't know, the Sherman antitrust act has only two key paragraphs (and six procedural paragraphs).

> Sec. 1. Every contract, combination in the form of trust or other- wise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is hereby declared to be illegal. Every person who shall make any such contract or engage in any such combination or conspiracy, shall be deemed guilty of a misdemeanor, and, on conviction thereof, shall be punished by fine not exceeding five thousand dollars, or by imprisonment not exceeding one year, or by both said punishments, at the discretion of the court.

> Sec. 2. Every person who shall monopolize, or attempt to monopolize, or combine or conspire with any other person or persons, to monopolize any part of the trade or commerce among the several States, or with foreign nations, shall be deemed guilty of a misdemeanor, and, on conviction thereof; shall be punished by fine not exceeding five thousand dollars, or by imprisonment not exceeding one year, or by both said punishments, in the discretion of the court.

https://www.archives.gov/milestone-documents/sherman-anti-tr...

If we strip out the penalties, the words defining what's illegal are literally just "contract, ...trust..., or conspiracy, in restraint of trade or commerce" and "monopolize any part of the trade or commerce".

Given that ambiguity, it's inevitable that courts will essentially have to write the law themselves.

https://en.wikipedia.org/wiki/Consumer_welfare_standard

Maybe the judges are confused, but there was a shift in enforcement around the Reagan era. I also think "consumer welfare" in this context is taken to mainly maen low pricing. That is, if a monopoly causes higher prices, then we should go after them. The DOJ going after Google and Amazon is a bit of a return to the former standard. (Source: news programs I listen to such as The Majority Report.)