Inclusion debates/Why is Missy so hated?

Note: Please take it into account that I didn't watch (almost) all of Series 8 and 9. It seems that people really hate Missy/Mistress/Master for some reason and I just want to know why. Some of these people say "Turning The Master into a woman totally killed the character." if you are one of these people, please don't respond to this thread.