Ok I will ignore the insinuation that I am not tolerant of anyone with core moral values (also I dont think I have ever called myself a progressive you may want to check your intellegence on that one), and take the "learning from a soldier who beleives in what he is doing" bit. Provided the situation demands we talk about the war, I would listen politely to the reasons he believes in what he is doing, think on them, and then I would share the reason why think that the war was a mistake. Let him rebutt and then leave. I would try to avoid this conversation simply to avoid antagonizing someone who I respect (and who in all likelyhood has a shit load of combat training.)
Everyone has bias, yours is practically dripping in almost every word. I wonder if you believe that the Ann Coulters of the world are biased. The soldier has more real life experience to back up his oppinion which gives that oppinion more weight than the oppinions of the Ann Coulters and Al Frankens.
So yes I would listen to what he has to say and think about it, what more can one ask.
Iraq is probably the single biggest political issue right now. I suppose it would be possible to discuss it with out bringing up politics but such a dissusion would be incomplete without covering the political and diplomatic impact that the war has had.
Lastly I would ask you how you would deal with a soldier who served a double tour in Iraq, who believes that going into Iraq in the first place was a mistake.