That there were antagonisms between pro/against doesn't mean Americans were not empathetic one way or another, and the 'pro war' were as maligned by other side just as well i.e. 'war monger' etc..
While the popular justification for war was exaggerated, Iraq did have WMD, but more importantly, the geostrategic consideration for removing Saddam just isn't something that can be used in a populist context. You can't say "We failed to complete the mission in 1993, Saddam is operating a rogue regime" etc..
Remember that there was a 'no fly zone' over Iraq for a decade to keep the Iraqi Air Force down - this is arguably an untenable position.
If the 'post invasion' process were to have been better prepared for and planned and less direct political failure etc. I suggest people would look at it as a 'success'. My point being - the 'motives' are very tied to 'execution' in terms of our understanding of whether or not it was a good thing.
Most poignantly - the US wasn't trying to create a vassal, just the opposite. None of the Iraqi Oil contracts even when to American firms, during the occupational period US had considerable influence but would actually rather not. The US spent gazillions of dollars trying to 'get some kind of civil framework' going, which they accomplished, just barely so.
In hindsight it was a hugely bad decision, but it were to have been less chaotic than arguably it might not have been a bad decision.
Putin's decision to invade Ukraine is purely Imperialist, his objective is to 'erase' Ukraine.
If Ukraine had capitulated, sure, there would be less bloodshed, but you'd also see a nation evaporate, and, another 10's of millions of people living in another Russian Vassal s*thole.
Hundreds of thousands of dead and god knows how many maimed, starved, displaced would not give a flying fuck about what the US was trying to do. Go there and try to oopsy in the face of the victims and see what happens.
The 2003 invasion of Iraq? Quite popular in the US at first (opinion polls at the time of the invasion showed over 70% support); people who opposed it were frequently belittled, shunned, harassed, boycotted (remember the controversy over the Dixie Chicks?). The reasons for the war were essentially invented – weapons of mass destruction which could never be found, attempts to link the Iraqi government to the 9/11 terrorist attacks despite the fact that there was no evidence the Iraqi government had any involvement. Many thousands died in the initial invasion, and hundreds of thousands in the ensuing war which the invasion began – all due to a war based on lies. Sure, Saddam Hussein was an evil man, but the world is full of evil men who do evil things – many of which the US is happy to call its friends (such as the Saudi regime) – but was removing that man from power worth all the ensuing death and destruction and chaos, especially when so many other equally evil regimes were left in place? Most of the worst things he'd done (such as genocidal massacres of ethnic minorities) were in the past, and more limited international interventions (such as the no-fly zones) appeared to be succeeding at preventing further such atrocities.
I'm not saying what Putin is doing to Ukraine is the same thing as what the US did to Iraq – Volodymyr Zelenskyy is no Saddam Hussein, and certainly not the Adolf Hitler which Russian propaganda presents him as being – only that Russians are not quite as different from Americans (among others) as you are suggesting they are.