You are completely full of it. The fact that our taxes might be paying for military pay does NOT give us some sort of right to send them off as modern day mercenaries. The military is for the defense of OUR country, not people halfway across the world in a place most Americans couldn’t find on the map.
Mercenaries fight for any flag as long as that flag pays them, and that pay usually includes all the loot they can cart off. US military personnel aren't mercenaries. They're fighting for the Stars and Stripes. That they engage in warfare on behalf of our allies (treaty or non-treaty) doesn't make them mercenaries - we're merely leveraging local manpower and resources that would otherwise be used against us by the invaders of the country we're helping.
Not that there's anything wrong with being a mercenary, of course. The Swiss Guards were legendary for their tenacity - once hired, they were renowned for fighting to the last man. Gustavus Adolphus built an empire using what was, in large part, a mercenary force.