OK, I'm a lousy blogger. But there's a lot going on on my plate, more than I want to talk about, and reality intrudes. :-)
First: the goal of the insurgent is to win the hearts and minds of those he sees as oppressed, to radicalize them into becoming as he is. This means that for the insurgent, the use of terror, as long as it is either non-ascribable (anonymous death squads) or directly from the opponent, is a fundamental part of his panoply of tools. He needs to radicalize the population, turning them into terrorists themselves, in order to win. This means that everything is fair, in his eyes, as long as the hated, existing government and society is destroyed and he, as a revolutionary elite, can recreate society in the way that he wants. I'm simplifying here, but this is fundamental to the ways that urban terrorists operate.
In other words, the terrorist, the insurgent, doesn't give a rat's crap about how he achieves his goal: the goal is taking power. Everything else is secondary. This is part of the legacy that the generation of communist training of 3rd-world terrorists by the former SovUnion has left us: this is part and parcel of how the Sovs trained their useful idiots to destabilize countries in order to achieve the revolution. If anything, you targeted the opponent's morality directly, get him to do terrible things in order to drive a moral dagger into his heart to destroy his will to resist. If he didn't do it, if he was strong enough to refuse to be manipulated into blowing up schools and churches that you were using, if his soldiers were so good that they would shoot between the human shields in order to get you, well then you create atrocities and get useful idiots to make it look like your opponent did it instead of you.
Second: the goal of the non-insurgent is to win the hearts and minds of the people, to get them to collectively deny and reject the terrorists. This is heavily dependent upon the structure of society: if you have a largely intact society, this is relatively easy, especially if the terrorists really don't have a base to operate from and really don't have legitimate grievances (like Baader-Meinhof in Germany).
The problem is when the society involved is in tatters, as it is in Iraq, as it was to a certain extent in Vietnam. Then you have the joint task of reconstructing society **while** denying the enemy the necessary radicalization at the same time. This is much, much more difficult than what the insurgent must do: he must merely destroy; you must not merely prevent the destruction, but also aid in the reconstruction.
This is part of the asymmetric nature of the conflict. It's not just that one side has all the neat toys and walks the walk, forcing poor Mr. Terrorist to hide and skulk (a rather irresponsible romanticizing of how terrorists work!); it's much more that Mr. Terrorist has a vastly simpler job, of using terror and the ensuing intimidation to dominate the situation. That's his advantage in the asymmetric side of the story.
So, given this, the key question becomes: are we even talking the same language here? Those perpetrating terror see their aims as being absolutely just, of having perfect and indeed moral certainty that their aims are just, that the society they are destroying is not one that is just and therefore MUST be destroyed (otherwise they'd not have bothered!).
But their goal is the destruction of the existing system. That is the difference, the fundamental and core difference. They are not interested in the niceties of restoring pre-war borders, or of returning territories once lost, or stopping genocide, or any such goal. They are only interested in destruction and acquiescence, and indeed have moved violence from the military to the population in order to force the issue.
The difference is fundamental: on the one side you have existing societies with their inherent problems, contradictions and conflicts. Wars may be fought, but tradition has it that you have a winner and a loser and that you no longer behave like a barbarian, slaughtering and depopulating in order to destroy your enemy.
On the other side you have the destroyers and nihilists, those who hate societies so much that they will do literally anything to destroy their structures. They are, literally, outside the realm of civilization.
And failing to see the fundamental difference between the two is an act of appalling political and cultural blindness.