the humans killed asriel becuase of them, chara tried to make asriel attack the humans when he absorbed their soul, and asriel didn't want to kill any humans
HEAD CANNON THEORY IN UNDERTALE CHARA THE FIRST HUMAN AND WAS A FRIEND OF ASRIEL... AND ASRIEL DID MENTION ABOUT HER SAYING " SHE WAS NOT A FRIENDLY HUMAN"; MY HEADCANNON IS THE CHARA WAS YES EVIL AND NOT GOOD BUT SHE WAS A SOFTIE FOR ASRIEL BUT SOMEHOW AFTER THE HUMANS KILLED ASRIEL SHE WENT ON A GENOCIDE AS REVENGE AND THAT'S WHY SHE HATES HUMANS