Anti-competitive behaviours such as price-fixing and over-broad no-compete clauses can be problematic even without a monopoly.

Fair point, though they typically only become problematic (aka are acted on/legislated against) when they significantly distort the market to a degree people start really complaining about it.

Usually due to either a monopsony/cartel/monopoly which controls most of the market doing it successfully.

If the companies in the lower 5% of a market price fix or the like, no one usually cares. Even 20%, usually.

The Sherman antitrust act speaks about ‘restraints of trade’ because it has to actually restrain trade, which requires a significant degree of control - which a successful/actual monopoly, monopsony, or cartel can do.

Technically, even attempting to do it is illegal, but going after every company that tries has a bit of the same feel as locking up every single toddler because they took a swing at someone or threatened them with their cute little stubby kid scissors.

It’s a waste of resources, not in anyone’s interest, stops behavior most people would consider necessary/healthy to some degree, causes much worse problems than it solves, etc.

On the other hand, locking up a successful serial killer is just good public policy.

The difference between the two is more a matter of the success and effectiveness of their tactics, not really intent.

Generally agree. There are some subtle edge cases like price dumping, but even that's still ultimately an attempt to gain market dominance.