Sexism is structured institutional oppression based on gender, i.e. of women, misogyny is hatred of women occurring in the above context, and racism is structured institutional oppression of racialised groups.
I don't think there's any such thing in our society as structured institutional oppression of men, so by using this word, we offer the recipients of man-hatred special protection from oppression that doesn't exist.
I think the concept of "misandry" gives fuel to the loud, obnoxious "what about men's rights??" reactionaries which dominate reddit. It comes from an idea that individual acts of hatred against women are somehow equivalent to individual acts of hatred against men, which they obviously can't be in such a pervasive atmosphere of cultural women-hatred and structural, institutional oppression of women.
Let's not give credence to this term, and let's be hated by the people who don't understand the above. At least we're being honest.