My critique of this essay is that Eco implies that it is a contradiction for there to be an external enemy which is overpowering and humiliating, and yet at the same time easy to defeat if our people would just stand up to them. That is not a contradiction. If a people have been demoralized and degenerated, it is actually very easy for them to be in such a state.
A really great example of this phenomena is China.
A century ago, the Chinese were indeed oppressed by foreigners, who humiliated and dominated them. However, these outsiders were paper tigers, when the people were united and stood against them. The only reason these foreigners were oppressing them was because of the weakness of their leaders, compromising with the outsiders instead of kicking them out and putting up walls.
China is a Fascist success story, and it undermines Eco's essay.
Indeed, many anti-colonial struggles can be described that way. Foreigners ("immigrants") oppressing a local population in collusion with corrupt local elites and chieftains. And an indigenous population too divided to do anything about it. Fascist scholars would say that Fascism would have protected the American Indians. Plenty of Black nationalists like Marcus Garvey were actually self described Fascists, and wanted to use Fascism to resist European colonialism.
Indigenous tribes that have had their social fabric and identities compromised by foreign influence and corrupt elites allow themselves to be colonized. Usually it is capitalism that corrupts them. A flood of cheap goods completely undermines them, and destroys their way of life. They almost always outnumber their oppressors, and if they could just reclaim their sense of national identity, they could easily rise up and take back their country.
Anyway, I'm not saying that I agree with Fascism, but I do think that Eco is presenting a straw man of it, which is not a good thing if you are opposed to Fascism and want to defeat it.