You're wrong on that. I've been a dues-paying LP member for some 15 years. While most bloggers who enjoy calling themselves libertarian favor war, a clear majority of card-carrying, dues-paying LP members favor peace.
Info source: Libertarian Party News [the national LP newsletter], January 2003, Page 23, "The Pulse":
...LP News readers disagreed with the assumption that a first strike on Iraq is unlibertarian. Loudly. In fact, fully 45.5% of respondents said they support such military action...[caveat: unscientific poll]...Meanwhile, another 45.5% of readers agreed that the party should work to stop an attack on Iraq...and 9% gave ambiguous answers, or said the LP should duck the issue altogether.
Let's hear it for the ambiguous 9% ;-)
One of the attractions of the libertarian view is that it is possible to work out one's position on most issues from first principles; this is easiest to do with complete information regarding direct causes and effects. Unfortunately in this case we have incomplete information and indirect causes and effects. Personally, I believe that Iraq has been supporting terrorists for years, and even exporting terrorism to the US on occasion. In addition, if Iraq was behind the attempt on Bush-41's in Kuwait a few years ago, that alone was an act of war.
Therefore we're already at war with Iraq (and others to be announced as we go along, of course), so we should finish it before Saddam gets any stronger. Perhaps this will inflame others to seek retribution, perhaps this will influence others to seek more peaceful means of cooperation, perhaps it will inspire others to throw off their repressive regimes instead of blaming their troubles on us. Perhaps it will set off Armageddon. Or perhaps it will prevent it, for a while. Such considerations are infinite and yield nothing but analysis paralysis; IMHO time is not on our side.
I don't like where this might lead [c.f. Orwell], but see no alternative at present that is not significantly worse. The problem with waiting for a 'smoking gun' is that it usually means someone got shot.