Why christians worship 3 gods ( if we don't count saints ) and ban polygamy?

@Smaran Cartlidge: We care because Christian influence is not something we can just turn off or switch channel from! Christians gets appointed to a school-board; and suddenly we're not teaching science like evolution, but pseudo-science like "intelligent design"... or schools starts teaching teens "abstinence only", instead of how to have responsibly. Christians gets elected to the Congress or appointed to the Supreme Court; and suddenly women can no longer control their own bodies or choose what medical-procedures they want taken.