Why populism and nationalism are “evil”

The reason western governments denounce populism is because populism is implicitly nationalistic when it takes place within homogeneous/majority homogeneous nations. And nationalism itself is virtually the antithesis of the current establishments and their platforms. They’re absolutely fucking terrified of it.
The same thing goes for identity politics. Highly dangerous stuff if practiced by the “wrong” group. Any basis for social distinction is liable to be deemed a catalyst for inequality. So, in typical Marxist fashion, things like race, ethnicity, culture, and heritage are, if not pathologized, then redefined as “social constructs” in the pursuit of social ambiguity, so that everyone is normalized, and nobody has an inherent claim to superiority (except for the Jews*, who are God’s chosen people, you racist anti-Semitic Nazi!).
But that’s not how the world works, nor has it ever worked that way. Egalitarianism is an artificial construct, and an instrument of pacification. Nepotism, being a natural function of the evolutionary selection process, is an inevitability, and always boils down to, if not family, then the next closest things: A common history, a common culture, a common tribe. A sort of greater extended family.
But with unchecked egalitarian liberalism being so pervasively interwoven with political platforms and corporate consumerism, both politicians and marketers alike literally can not afford to compromise the number of votes/customers they stand to receive if they just keep their mouths shut, play it safe, and endorse the path of least resistance for all. So political correctness becomes their mantra out of necessity, and as a result, they are bound to virtue signaling, moral posturing, and noble rhetoric. And what you get from that is a paradoxical vicious circle of regressive “progress”. State enforced radicalized tolerance. A system that emulates corporate consolidation, trudging on in the pursuit of capital at the expense of distinction, for anyone who operates within it must give way to assimilation.
The irony is that the end result is the greatest inequality of them all. That same old, pyramid structured model of oligarchic capitalism. Those at the top shout down to the ones at the bottom not only whatever they want to hear to pacify them, but they also work hard to transform them into more efficient workers. Part of this involves convincing them that their self-affirmation/actualization is co-dependent on their willingness to deconstruct their identity.
Because machines work most efficiently when all the components match.