Again, while it is convenient to label them as "irrational" - particularly as we can then use that label to rationalize doing whatever it is we happen to want to do - it is simply not so. Whether their goal is real or attainable or practical or not is all neither here nor there - it is their goal, and it is what motivates them. And they act in a calculated manner, designed to advance that goal.
You did not address directly the question of cultural relativism in foreign policy. There are certain human freedoms that are universal.
Such as the "freedom" to have universal, cradle-to-grave health care, the "freedom" to breathe air that is 100% free of fossil fuel emissions, the "freedom" to advance in society according to the historical victimization of your particular ethnic group. Your argument is wonderful, so long as everyone agrees what those universal freedoms and rights are. Of course, if everyone agreed about what those universals were, we wouldn't be in this kind of mess in the first place.
But, of course, they don't agree, and so it's simply a game of who can impose their universals upon the others. You will notice, I hope, that nowhere do I deny that such a universal morality might exist - what I am telling you is that it is irrelevant. The truth doesn't matter in politics, whether local, national, or international - what matters is what people believe. And most people simply don't believe in your conception of universal human rights, so you have little choice but to simply impose it upon them - "we know what's better for you than you do".
But, the cry goes out, we have the forces of truth and justice on our side! Wonderful. The communists say exactly the same thing. The Islamists say exactly the same thing. I don't claim for a minute that all cultures are equally valid and moral, but in this argument, there is no difference. Everybody says that they have the right to impose upon another, everybody says that they have the right to violate some rights in pursuit of others - what makes you different from them? Why is your cause just, and theirs not? Because your ends justify those means? What happens when they make exactly the same claim?
It is the United States vs the American Indians. Two cultures that were antithetical to one another and, because of their nature, could not co-exist. One was a nomadic culture, the other based on a settled agriculture. One subscribed to the concept of private property, the other to communal property -- which becomes impossible when both are claiming the same property.
In this particular case, neither was devoted to the extermination of the other. Instead, the Indian Wars were about preserving one culture vs imposing another culture.
It is possible to construct a moral defense for either side of this particular culture war. One can argue who was right and who was wrong. But one cannot argue the outcome: one culture prevailed over the other. From a practical standpoint, one culture was superior to the other when it came to the issue of survival.
We (and the world) now find ourselves confronted by another culture that is antithetical to our existence. The Radical Islamists want to a.) kill us or b.) convert us. Seemingly, if they had their 'druthers, they 'druther the former. This is where the analogy with the American Indians breaks down -- they did not undertake to exterminate the white man, nor did they wish it. By the same token, the white man had no interest in extinguishing the Indians, merely subduing them.
Co-existence, the strategic equilibrium that was achieved during the Cold War, is not an option under these new circumstances, though. Just as the culture of the Arapahoe and the Cheyenne could not co-exist with barbed wire fences and wheatfields, the Radical Islamists cannot co-exist with Western Civilization.
Thus, the morality of the War on Terror is moot. It is not really a question of right or wrong. It is a question of survival: Kill them before they kill us. Kill them while they are still a relative few, before their movement expands further.