Why is the use of terminology in reference to Ho Chi Minh's forces important for the Americans and South Vietnamese to establish?

The name "Viet Minh" equates to "Freedom Fighters" in the minds of the Vietnamese people, due to the fact that Ho Chi Minh's army was successful in liberating Vietnam from French rule during the First Indochina War. Thus, it is important to re-frame the term to paint the communist forces of North Vietnam in a more negative light, i.e. "Viet Cong", to prevent larger numbers of peasants from joining the communist cause.