I agree with most of what you have to say, but there are some who volunteer for the military because they want to ensure that if in the unlikely event the United States does face some sort of external threat, there is a force in place to defend against that threat. The standing army also provides a means for deterring threats like that from coming up in the first place. These people dislike the "international adventurism," but are willing to put up with it for the reasons given above.