Yes, I cannot see the USA totally destroying a country run by a threatening regime, if the only thing it has done is be "threatening". I can see us destroying in total warfare a country we are in open warfare with. The model of WWII would fit, and would be appropriate.
In my opinion, what was done against the axis powers in WWII was terrible, but appropriate. Their civilian populations were supplying the war machines that were killing our citizens, and if they could have done to us what we did to them, they would have done it, and with prejudice. It was a war of survival.
I do not think, even for second, that the majority of Iraqis are against the USA and are actively supporting the terrorists. I do think there are a large number, perhaps a majority who are afraid to actively take a side, especially if doing so can mean having your head sawed off slowly with a rusty knife with your body dumped on your doorstop for your kids to find. It is remarkable that are are a number of them who HAVE tried to step up. We shall see. Perhaps we will fail. But we saw how well that whole hands-off thing worked before 9/11.