Redleg you bring up some valid points but again, I think all of them are answered, and if not answered made better, with US forces withdrawn.

Does a nation that goes to war and topples another's regime have the obligation to attempt to protect the people of that nation?
Yes, which is exactly why I state the US should withdraw their forces. That act is better for the Iraqi people than any tinkering, bombing of insurgents, initiatives etc.

There is enough other nations, far less maddening for the Iraqi people who would be willing to put in the extra troops / commit troops for the Iraqi govt. On top of that, although you dislike it, the UN would get more involved, I am sure.

Not to mention the progress with the Iraqi govt forces is getting better - albeit slowly - and they can take over far more operations / control.

If one nation destroy's the infrastructure of the defeated nation in the warfare that commenced - does that nation have the obligation to rebuild the infrastructure so that the people can return to their quality of life?
Again the situation is made best with US TROOPS withdrawing. US companies - however much I dislike it - can help rebuild the country and US technical people can help the Iraqi govt, but I fail to see why the US TROOP presence is needed for this. As stated their presence can be filled / covered.

Plus building a new infrastructure is surely better when the new infrastructure you create / the old infrastructure which remains, is not under almost constant attack. The attacks will go down with the US troops out.

Also remember the major infrastructure has already been made, the govt, Iraqi troops etc are in place. That is the hardest thing.

Do you honestly think that the second that the United States withdraws from Iraq that the violence will all of a sudden stop?
No. Not in the short term anyway. When the US withdraw I would suspect bombings would go up. However after that I am sure it would drastically go down. The major factor influencing the insurgent movement? The US in their country. Simple as that. They list it time and again as their major factor in their broadcasts and their bombings. Plus many Iraqi people have some form of sympathy with the insurgents even though they kill innocent Iraqis because they too don't want the US in their country. They do not necessarily support the insurgents but they are definitely against the US staying as long as they are - so they have an aversion of confronting and helping the Iraqi govt defeat the insurgents. With the US out, this will change.

It might not be the best solution in every situation, but over all it is the solution which fits all the problems best.

Oh and the analogy works better with unbreakable, unbendable metal bars then.