Polygamistic families create an atmosphere where children are neglected by their fathers(as polygyny is the most predominant form of polygamy I would rather use that as the example. Polyandry is very rarely seen.). There are also more allegations of incest, abuse, and forced relationships. Primarily sourced from those who have left the polygamist groups. There are also many who live in poverty because of the limited resources, and primarily due to the nature of these societies to be male dominated. Women are generally NOT treated on an equal level as the men.
Source: Polygamy in Canada: legal and Social Implications for Women and Children – A Collection of Policy Research Reports
As for greater numbers equalling greater potential for conflict. I would think the ignore feature on message boards tends to prove that.