Polygyny is permitted in several religions and it has been practiced legally in many parts of the world.
Polygyny has many benefits to society, such as pooling of resources and increased marriage rate. The children have several step-mothers and many more siblings than other families, resulting in stronger family ties.
Prosecution of families involved in polygyny is oppressive and amounts to a restriction of personal liberty, and a violation of freedom of religion. Polygyny does not harm any of the parties involved, but rather it benefits them.