Do you support the legalisation of polyagmy and polyandry

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Two women agreeing with me and each other to constantly get me in between a titty sandwich every night? I can see the benefits.

Seriously, if all parties involved agree to it, go to it. But no further tax benefits should be allowed to them beyond what normal married couples would get.

Well, that's the only thing you'll ever agree on, friend. Obviously the sating of your carnal desires does not constitute a real marriage.
Besides, how do you hope to actually feed and clothe them all, and feed and clothe the children that you might get from them?
Polygamy is a zero-sum game, if you do not live in a society where this type of marriage is the norm.

I don't think it should be illegal, unless of course there are consequences of which I am not aware. The thing I don't get is why women would want to be in a polygamous relationship(I understand why an egotistical male would). Marriage should be about the parties involved having equal say and involvement in the relationship, and I don't see how that is possible with a polygamous marriage.

They don't. I can tell you from personal experience that women do not wish to be involved in such a "marriage". Therefore it's usually done by forcing the old wife into accepting the new wife. Even if you don't force her, she simply accepts, as she can't really do anything else if she refuses.
Similarly, a woman who is afraid of losing her husband might consent to it without approving it.

Do governments have any right to dictate what consenting adults can do with their private lives? No.

Marriage is a public affair. I would certainly not care if a man had a wife, and a mistress on the top of that wife, and they casually get together to have fun, if they are into that sort of thing, but marriage is certainly something beyond than just having sex, isn't it? It's about being able to live together, and being able to raise a family together.
Today's standards in the modern world are in conjunction with monogamous marriage. Polygamy may exist outside of marriage, and even there, many people would disagree with such a thing.