No, fight polygamy, and reduce welfare.
You want a harem?
Rock on dude! Take all you can afford.
But, assuming their human, and female, you're married to one; the rest are whores.
What next? A libertarian arguing for parents right to bargain their children in prearranged weddings?
Why do you assume I want a harem just because I'm in favor of free adults freely choosing their relationships? It's like saying that someone who wants to legalize pot wants to smoke it.
There are legitimate laws against children for a reason, they are not capable of freely making choices for themselves and have less free will than the rest of us.