You could say that monopolies are inherently bad because they stifle innovation even if they don't lead to higher prices. An unassailable monopolist has no reason to innovate because competitors are effectively locked out.
But it appears to me that there is a psychological bias towards an exceedingly narrow definition of substitution goods and therefore markets, especially in digital technologies.
For instance, Microsoft clearly has an extremely dominant position in PC operating systems. The market for PC operating systems used to be synonymous with personal computing, but that is no longer true. Mobile devices now dominate personal computing.
So Microsoft has lost most of its monopolistic power without ever losing its dominance in the market as it was originally defined by regulators and users.
Similarly, search used to be synonymous with using a web search engine and Google clearly has a monopoly there. But now we search Facebook, Amazon, Netflix, etc for various specific things in different contexts and Google has to pay billions to buy users from Apple.
So my point is that yes, monopolies are inherently bad, but they are also inherently unstable in ways that are not adequately reflected in the current thinking around anti-trust regulation.