" Mass mobilization in Iraq against US-British forces will be at most a nuisance - easily suppressed by the ruthless employment of massive firepower. "
This statement is unfortunately erroneous. It is indeed true that mass mobilization in Iraq would be easily put down by superior US firepower. In fact, the US would welcome that scenario because it'd finally give a chance for US firepower to have a medium-sized target that our attack helicopters, jets, and artillery were designed to annihilate.
However, the statement is incorrect and misleading on several points.
First of all, the US would be fighting a two (or three, depending on if you separate Sunni nationalists from jihadis) front war, with the additional front being the Shia, who have up to now been on our side (or at least complacent). This would be a very difficult situation for several reasons, the most pertinent being that Shia compliance is ABSOLUTELY CRITICAL to OIF success. Not only do they comprise 60 % of the population, but they also control the only seaport (Basrah-area) from which Iraqi oil flows - which itself is, or is going to, allow for the Iraqi's to take over sovereignty. If this is lost, Iraq becomes unwinnable, no matter what your definition of victory is. There are around a dozen US Navy warships and Coast Guard vessels right now protecting this port, in additional to a couple British tank divisions. No, our superior firepower cannot protect the entirety of the al Basrah pipeline from a simple sabotage, each one taking around a week to fix. This all is overlooking the government effects, insurgent threats, and small to large scale sectarian conflicts that would ensue and would most likely cause a true civil war in Iraq. On that point alone, the author has it gravely wrong.
Secondly - and perhaps more disturbingly - the author overlooks the main threat to US troops from Iranians: medium range ballistic missiles fired into our literally city-sized base camps. Casualties here could range from 5,000 to 20,000 easily - and that is assuming the Iranians fight fair: no chem/bio attacks. Forget Iranian tanks regiments, air force, etc - these are all preventative forces (opposing, in all honestly, a Saddam led ground invasion), yet still able to kill US kids.
So, without even going further, the author's error has miscalculated or underestimates about 30,000 US deaths - almost a fifth of our force. He is not wrong in that a mass buildup of any force, be it Iraqi or Iranian, would be destroyed quickly. Yet it is a critical error.
His points about the region at large are also, theoretically, true, yet they overlook enough points to probably account for about another 10,000 to 15,000 casualties and a few more decades of conflict.
Here's my frustration. The author's presentation, which is indeed based on prevaling wisdom, is not at all an accurate picture of how difficult this war would be. Unfortunately, thus far, most editorials paint this war as a combination of JDAM strikes, cruise missile attacks, and bunker busting bombing with some anti-aircraft facility destruction in between. This is very, very simplified.
My point being not to criticize the author, but to hopefully disprove his (and indeed general) beliefs that this would be, if not an easy, then a one-sided war.
The thread title is inaccurate, yes, we would not occupy Iran like we do Iraq, but if the war is not over in two weeks it will not be over in four or five years. If the victory is not decisive and swift, the war will most likely be larger than Vietnam - and very different.
It is my sincere belief that, if it comes to it, we will use multiple tactical nuclear strikes against Iran. If you find this option incredulous (however immoral or counterintuitive), I sincerely believe you are unfamiliar with military realities. But all of this said, war and rumors of war should be feared, regardless of the side - it is a very serious situation. There will be little armchair quarterbacking in this one. If the war is not over very quickly, a lot of people kid's on both sides will die and a lot more will see combat. Keep in mind, I'm saying this having active duty friends and being of combat age myself. The situation is very serious.
Let's hope (and pray, those of us who pray) that diplomatic pressure is successful. It is exponentially better.
-- my apologies if this seems too melodramatic (nevertheless, I think the logic stands)
Cheers,
James
PS - I think there are one or two other viable military options that are also available and have a good chance of success, but I don't feel inclined to mention them. Not to say I have any special insight, much less a job. Hehe.
but if you don't mind before jumping in and saving the free world would you check first with us to see if we need saving. 
It was Churchill's contingency plan if the Germans invaded Britain. Given the fact the Irish had spent the last 700 years getting rid of the Brits they wouldn't have been exactly welcomed. The second world war started over Britain's concern for her empire. She declared war on Germany for purely selfish reasons. It wasn't until the war was nearly over that people realized what Hitler had been up to in the death camps and suddenly that was being portrayed as the reason for the war. In fact Hitler had many admirers amongst the elite of Britain.