What if we were to look at the Calormenes as representative of governments that are more or less repressive?
The Narnian monarchy reminds me a bit of the British monarchy. There seems to be a great deal of democracy practiced in Narnia as well as religious freedom. Notice that the citizens of Narnia "worship" Aslan in their own way without theocracy in place to dictate dogma, etc.
The Calormenes not only have a very rigid government and strict (controlling) hierarchy, they appear to have both a controlling theocracy that completely supports the overbearing government. We can cite examples of this type of government throughout the world and throughout history without specifically limiting the examples to the Middle East: Asia, Africa, and even Old Europe.
I may be stretching the point a bit, but we notice the theocracy is first introduced into Narnia in the Last Battle. The Ape is supported by the Calormenes.
Tash may represent all things that are not necessarily Anti-Christ in the strictest sense but all things that become stumbling blocks to knowing Christ. Tash could represent such things as power, money, blind dedication to a cause, etc.
I agree that Lewis was not a supporter of Universalism, but at the same time, I don't think he was ready to close the door on human beings who cannot, for one reason or another, come to Christ.
One additional thought: it is rather interesting that being that Aslan is a lion, animals could readily identify with Aslan as being God. If we humans in this world were to start worshipping/following an animal, we would be accused of worshipping/following an idol. The Calormenes "created" a god who would look more or less human, even though it had a vulture's head and four arms. The illustrator Pauline Baynes even gave Tash legs with claws, probably representative of power, terror (a god to be feared), demanding strict obedience or else. I may be getting a bit deep here, but when people act like Calormenes and take on a god to worship, we may then feel that this god is very demanding, overbearing, a slave-driver, et al to the point where we feel "lost."