OK how about the similarity of attempting to use the military in a situation where, for the most part, we are not fighting against a military, supporting a "government" that only exists because we propped them up, supposedly for the benefit of people who mostly wish we would get the fuck out.
Yes, there is a good comparison between the Gulf of Tonkin, the Maine and the Lusitania -- and all have a great deal of similarity with the alleged implication of Iraq in 9/11 as well as the claimed WMDs. So, if your point is that there are other parallels that could also have been drawn, yeah you are right, but since not many people can really relate to how we got into the Spanish-American war, Vietnam seems a more meaningful comparison.
There is no conceivable way to achieve a military victory in Iraq because it is not a military problem -- much like Vietnam. So, just like in Vietnam, there is no conceivable way we can win, or even any idea of what "winning" might involve. Can you spell "quagmire?"
True, FDR did not know exactly how he would defeat Germany and Japan, but he did know he would be fighting against German and Japanese military forces. It was reasonable to assume that it was gonna take military force to defeat them.
As for lack of respect for troops, I am not suggesting that anyone (at least not significant numbers) does -- but that any one not supporting the president's position is accused of doing that.