If by polygamy you mean relationships among more than 2 people, I'd say that monogamy used to be important in regulating western society in the past (with the man and the woman having different roles, the former was in control and went to work, and the latter was relegated to taking care of children and the house).
However, that's no longer needed. I'm myself in favor of rights to people in consensual polyamorous relationships
God Dammit, you ruined my argument.
Anyways, there are a lot of things that are considered illegal that, to me at least, lack rationality altogether.
Also, I'd say it's incorrect to suggest that religion hasn't played a part at all in shaping morals.
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In France the main Left-wing party is the Socialist party, and at the left of that are the Communists.
Yes but both views are still separate.