It harms whole societies and leads to social breakdown.I have nothing against polygamous marriage because it do not harm anyone .
Stress, quarrels and neglect: the 'normal' polygamous family
Why Polygamy Is Bad for National Security
The impact of polygamy on women's mental health: a systematic review
HARMS OF POLYGYNY - Polygyny and Canada's Obligations under International Human Rights Law
Anyway, I can find a bunch of articles and studies saying much the same things about it. Monogamous marriage has proven to be the best arrangement for women, children, their families and society as a whole.
The puzzle of monogamous marriage