I see your point, but it is not quite that simple. I agree the Iraq was was totally unjustified. However, one joins the armed forces not knowing what he will be ordered to do. What would you have someone do who was in the army, opposed to the Iraq or some other war, but is ordered to go? Quite a dilemma, no?? Do you go and support a cause you think is not just, or do you refuse and perhaps ruin the rest of you life by disobeying a direct order. Easy to say one should follow his conscience, but not so easy when it comes to doing it. So are we supposed to withhold support to someone who was ordered to fight in a war we, or even the soldier himself thinks unjust? I dont think so. OTOH, I am somewhat put off by someone saying "thank you for your service" to a stranger they dont even know. I think that acknowledgement should be reserved for people you know and are aware of what they did.
Ironically, now that members of the armed services are volunteers, and not forced to join, they are highly respected, while during the Vietnam war, when one had no choice but to go, they were pretty much universally hated.