You're making the mistake of thinking that this amount of resources and effort was available in some kind of global pool to be allocated to anything, anywhere.
The truth is that aside from maybe the human effort this would've gone to some other war or battle or simply be left unspent.
If, on the other hand, you're making the observation that war and violence sucks and that humanity would ultimately be better off if we tried to work together. Then absolutely I'm behind you 100%.
The "global pool to be allocated to anything, anywhere" is called the economy. When concrete is not needed for walling people in, Iraqi concrete factories don't work extra shifts. The people who would have had to work there become employed at other jobs.
In the short term, a soldier who doesn't have to neutralize Sadr City probably does get assigned to some other war mission. In the medium term, his unit is not called up again and he returns to auto mechanic or whatever other productive thing he can do. He puts his effort into raising kids instead of raising barriers.
The truth is that aside from maybe the human effort this would've gone to some other war or battle or simply be left unspent.
If, on the other hand, you're making the observation that war and violence sucks and that humanity would ultimately be better off if we tried to work together. Then absolutely I'm behind you 100%.