Polygamy almost always occurs in the form of polygyny, and the societal impact of such a practice becoming widespread is highly negative. Here's what it results in:
1) Diminished standing for women.
2) A surplus of unmarried men.
In the face of problem 2, the options are either getting rid of the extra men/boys (Fundamentalist Mormons), or having a violent, unstable society. Neither is particularly desirable.
If you believe that one of the functions of the state is to encourage a stable society, the adverse consequences of the practice are significant enough to easily justify criminalizing it.
Slashdot Mirror
Polygamy almost always occurs in the form of polygyny, and the societal impact of such a practice becoming widespread is highly negative. Here's what it results in:
1) Diminished standing for women.
2) A surplus of unmarried men.
In the face of problem 2, the options are either getting rid of the extra men/boys (Fundamentalist Mormons), or having a violent, unstable society. Neither is particularly desirable.
If you believe that one of the functions of the state is to encourage a stable society, the adverse consequences of the practice are significant enough to easily justify criminalizing it.