I agree that protecting Donbass is one thing, but there was no shock and awe as when the US bombed Baghdad before sending the troops in. Kiev was spared all that, although there was some bombing, it wasn't what it would have been if Russia intended to take Kiev from the start. Going in Putin said he was denazifying Ukraines army and securing the regions of the breakaway provinces, the ethnically Russian portions of eastern Ukraine that broke away after the Maidan coupe, the regions that Kiev has been bombing since 2014. It appears that Putin resigned to the fact that Ukraine was joining nato so he decided it was time to move the Russian border over a couple hundred miles westward.
One way of viewing it is that Ukraine took a bit too much land when it broke away from Russia in 1991, after the collapse of the Soviet Union and now the border is being adjusted. Personally I don't care where the border lies between Ukraine and Russia, I would like to see the lines drawn and the fighting come to an abrupt end.
There did appear to be an early attempt to grab Kyiv, when that long armored column ended up getting stuck. That seemed like an ill-fated operation. It just didn't seem they had enough force to take all of Ukraine all at once. Plus, the internal rot and corruption within the Russian government and military was laid bare, as the kleptocracy practically gutted their armed forces and hobbled their war-making capability.
I don't know how much planning they put into it, nor what it was that caused them to move at the time they did. The way it came about, it almost seemed like an impulsive, panicky maneuver, as it didn't appear to reflect any careful, calculated, long-term planning.
Whether he may have been goaded or provoked into attacking is hard to say, but by invading Ukraine and engaging in aggressive warfare, he has violated international agreements (Kellogg-Briand Pact) and the UN Charter. Despite whatever reason there might be for doing so, at least when looking from an international legalistic viewpoint, he broke the law and violated international convention.
It was different with the U.S. against Iraq, the West could easily justify their position because Iraq also engaged in aggressive invasion against Kuwait, so the U.S. could easily justify an attack on Iraq in the eyes of the UN and world community. In 1991, when Iraq agreed to pull out of Kuwait, the U.S. agreed to a ceasefire which lasted until 2003. Some people (including the aforementioned Col. MacGregor) were critical of the U.S. disengaging in 1991 and felt they should have gone all the way to Baghdad right then and there. If nothing else, it would have saved America the trouble of going back there in 2003.
Sometimes, it's hard to fathom how the minds of U.S. policymakers actually work. Even if we assume that they are good-hearted and have the best of intentions (which they don't), the problem they're facing is that, however well-intentioned their motives might be in "helping" other countries, they invariably get intimately involved in the intrigue and internecine rivalries of whatever country or government they're working with.
If we're going to set ourselves up as some kind of righteous, international policing authority, then that would still require a certain degree of detachment and objectivity. When police officers lose objectivity and get personally involved in a case, then that's a breach of professional ethics. It seems it would be no different on the international stage - except the stakes for failure are much higher.
In a way, that's how the West's approach has developed regarding Ukraine and Russia. Legally, the borders were established when Ukraine was a Soviet Socialist Republic, and the USSR established the boundaries of that Republic. When the Soviet Union dissolved and every Republic legally seceded, then what was once the Ukrainian Soviet Socialist Republic then became part of a newly independent Ukraine. If I recall correctly, Russia and Ukraine signed an agreement in 1994 confirming and recognizing those boundaries as valid. One could argue that, if the Russians had any misgivings about the borders, that would have been the time to bring it up and voice their concerns. They didn't do that, so in the eyes of the West, that agreement has the force of international law.
So, in the West's eyes, they see it as an open-and-shut case, with Putin being declared the guilty party who should be arrested and put on trial before an international tribunal. At least from that standpoint, Putin is as guilty as a cat in a goldfish bowl.
Of course, such a view might be seen as too Western-centric and doesn't really take into consideration the root causes and the long-term historical circumstances. Maybe some mistakes were made in the early 1990s and the Russians felt they got cheated. Perhaps some buyer's remorse that could have been addressed sooner. There's also been apparently a great deal of bad blood and resentment built up between Russians and Ukrainians which have their roots going back centuries. I think if more people took the time to understand the history of the region, it would be a lot easier to understand why the Russians see the world as they do.