"Iraq exists only as an idea, not a nation." What do you think of the author's assertion?

Yup ... dead on.
Iraq never really existed until 11 November 1920.

The British established the "State of Iraq" under the Hashemite king, Faisal I of Iraq, who had been forced out of Syria by the French.

British authorities selected Sunni Arab elites from the region for appointments to government and ministry offices.

Iraq is approximately 60-70 percent Arab Shi'a, 20-30 percent Arab Sunni and 10 percent Kurdish.

Iraqi Kurds are mostly Sunni, with about 10% being Shi'a Faili Kurds.

So from the get-go the west had enforced a minority rule of the area.
What could go wrong?

There are three nations inside the 'border' of Iraq. This was done intentionally by the Brits in Iraq and Afghanistan when carving up the old Ottoman Empire, but other also by Imperial Powers elsewhere. When occupying a foreign land its best to keep factions fighting one another so as to not fight the Empire. Find a roughly 1/3 minority, raise them to power to control the government, military and structures of power, make them dependent on you and they become fierce fighters to perpetuate the status quo against the other 2/3s. This all works until there is no Imperial Power to support that 1/3, or until you decide the strongman that inherited that 1/3 after the Empire needs his regime changed. Then the inherent imbalance in the 'country' you drew will eventually re-stabilize through war: it will either split along ideological lines into several sub-nations, or one group will rise to dominate the others (often brutally). ISIS/ISIL/Daesh knows their history, we seem to have overlooked it.
https://www.google.com/search?q=Sykes%E2%80%93Picot+ISIS+ISIL&ie=utf-8&oe=utf-8

This is some of the truest things I have ever heard about Iraq. I think it is dead on.

I think he is right; although how much our failure to support the Iraqi forces prior to their collapse is an open question. Our recent air campaign seems half-hearted at best.

The Iraqis have no history of an inclusive government that protects the interests of all sectors, and our premature departure allowed the country to descend back into sectarian infighting.

Without a strong hand guiding them toward the goal of a unified government and providing for their security until they become self-sufficient, I see no hope for the country to remain intact.

They may become a client state of Iran or perhaps they will be incorporated into the Islamic State if we continue on our present course.

As long as empires have created client kingdoms the same "tricks" have been used.
Draw borders that have nothing to do with tribal, ethnic, or religious demographics. Empower minority groups to overpower majority groups. The empowered minority cannot throw out the Colonial power, because they will lose their power. You cannot nation build when loyalty to other social groupings far surpasses loyalty to an artificially created nation.

First of all I want to make my point very clear to everyone. Including you Gunny Wayne A. Ekblad. Our CIC decided to invade Iraq because of the WMD that he was told to by you name it. We did the same thing for the Gulf War, Vietnam and Korea. All because of our Country's National Interest and more interested in controlling what the communist will do next. Please don't get me wrong, but all of our servicemen and servicewomen were directed to do what we are all trained to do, fight for our freedom from the evil countries involved in getting rid of us period. Especially with this particular war wiith Iraq and ISIS. I'm concern that our Leaders of Our Government is in disarray. Our military men and women of all era's should be very proud of what we did to accomplish our mission and freedom for others. But when you have and enemy who is willing to do nothing but to kill and kill again the buck got to stop somewhere and soon. Just my professional experience. James