Why is Mercy so hated?

Hey! Can someone explain to me why Mercy is so hated? I’m a mercy main and don’t really get it. I do get it when it’s a mercy with her eboy duo and healbotting etc, but why is mercy just as a character hated? Good mercy players too, who contribute to the fight. I do get that mercy is not the best support compared to bap or ana, but still? Why does everyone hate her so much? Please explain it without hate and just constructive criticism.