Then why even bother calling it "left" at this point? Just say they're anti-monopoly. Is there really nobody on the right who are also anti-monopoly?
Tbh classification that makes most sense is wealth level.
Ultra rich and very rich and rich and upper middle class and ..
Because the underlying beliefs of a 'left' anti-monopolist and a 'right' anti-monopolist are likely very different, and similarly their proposed solutions and view of an ideal society will also diverge significantly?
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Also, it should be noted that we lack sufficiently concise but specific terms to use instead, and because alternative terms that are used are relative, and open to interpretation.
e.g.:
Many political commentators currently use the term "populist" to describe someone who's somewhat divergent from the capitalist political mainstream (and in US terms, I'd include the current Democrat establishment and traditional non-MAGA Republicans in this group). But when the term is applied to people as diverse as Corbyn, Sanders, and AOC on the one side, and Orban, Farage, and Trump on the other, it's nonsensical without much more explanation.
Presumably because anti monopoly right is much less common? Or because the anti monopoly right is concerned with different aspects of monopoly?
If someone said they were anti monopoly, that the government should do something to prevent businesses from operating like that, I'd never expect them to be from the right to be honest.