Conflict can still exist in a world with solid communication and emotional maturity, because some needs are mutually exclusive and we are all limited by material conditions. Observe a living situation with someone who is sensory-seeking and someone who is sensory-avoidant, it's "fun."
Also, no communication is perfect, people misunderstand good intentions on the regular, often behavior is uncontrollably modified by illness, for some differences of opinion there is no objective standard to decide against, we don't always understand what drives our behavior, despite all our scientific advancement we live daily surrounded by things we don't know or understand, even when one is being honest another person can lack trust and disbelieve you, the list goes on and on! So many possibilities!
