It's a free country, and a two-sided market. Those who are betting on US success are just as much engaged in a mild form of war profiteering as those betting against it, though the former may feel less guilty about spending their money if they win. Neither group is materially contributing to the conflict, except perhaps in some extremely indirect way.
I'm sure you remember how, after 9/11, many were hoping for a "patriotic rally" and some were either promising to buy, or urging others to buy, just to "show those bastards." The idea reflected a misunderstanding of the financial markets, in my opinion. Moralizing over a correctly pessimistic market call likewise reflects a desire to turn the financial markets on their head, and ask them to reflect how we might like things to be rather than how market participants, rightly or wrongly, judge them to be.
It is possible to optimistic about the future of this country, or about the upcoming battles in Iraq, but pessimistic about the market, short- or long-term. The opposite is also true. Your friend's mistake may be to think that profiting from a correct prediction of political and military setbacks could make up in any significant way for the direct and indirect effects of such a turn of events. Even if he's the kind of person who can cheerily rake in his gains while the agonies of war and the costs of military and political failure are everywhere on display, his sense of good fortune may be very short-lived.
All in all, I don't like his trade simply as a trade. If I did, I might take it. I might even consider it the responsible thing to do, but I would take no pleasure in it, as I'd be too concerned about the future of everything and everyone I care about.