Why do many still today question whether or not Vietnam was worth it?

Many people question that topic since it was a CIVIL war.  The country was fighting between itself.  The U.S basically barged in and helped the side it thought was better.  So many people died during that war.  Many people believe that if Southern vietnam wasn't controlled by the U.S during that war and if the U.S had just stayed out of it then so many people would still be alive.  On the other hand many believe the exact opposite.  I hope I helped.  Pls mark brainliest:)