It seems like polygamy is bad for women, and women can lose use rights to some of their land when a husband takes a second wife. Should we advocate for legislation that outlaws polygamy?

In my opinion, laws against polygamy are ineffective at best and harmful to women at worst. Even though women very often do not want their husbands to take a second wife, and a second wife (and children) can stretch already limited resources, making polygamy illegal does not stop polygamy. But, if polygamy is illegal, subsequent marriages will be illegal and unregistered, and subsequent wives will have no legal rights to their husband’s income or assets. Second wives are often women who are vulnerable because they are young and have little or no income or choice about who they marry. I do not know who the “we” refers to in your question, but I think thoroughly understanding the issues related to polygamy for all women would be a critical first step. Where does polygamy occur? Under what conditions does polygamy occur? What is the attitude toward it in rural areas? Urban areas? What is the current law? What issues does the current law raise for first and second or subsequent wives? Who wants to change the law and why? What could the unintended consequences be? If polygamy, which was legal, is outlawed, the law should be very careful not to apply to current polygamous marriages—should not apply retroactively because that could be very harmful to women and children already in a polygamous family.