Why are these things considered immoral, unethical, sinful, etc.? How do you feel about them?
Well, I can't really lump them together and give one opinion about all of them.
I find marrying multiple people to be a negative thing. I'm not completely decided as to whether it's a strictly "bad" thing, or simply something that is just definitely not for me and hence I have a biased view. My largest complaint against marrying multiple people is that it seems to imply that one sex is inferior to the other (and usually it's one man marrying multiple women). It seems to suggest that the one man is not completely satisfied to love one woman, and so he can have several, but the woman should be completely content to love that one man.
I do, however, find it difficult to form a reason as to why it should be illegal. Making something illegal because one doesn't like it is not a justifiable reason. My concern is that polygamy seems to be practiced in some specific communities, so children growing up may be coerced into remaining in that culture.
As for polyamory, I am more forgiving towards it, as it is not necessarily imbalanced. It's just not for me, at all. The concept of having an extremely strong, loving relationship between two people is very important to me.
Well, I would have to ask, what would be the point in legalizing these things? At least in Western culture, for the most part, relationships have remained between one individual and another individual (of course there are exceptions, but it is a rarity). Since multiple partners is not really something that citizens have requested or care about, I would question why bring it into a political debate when there are so many more important issues to focus on?
I think it's the other way around. We shouldn't have to have a point to legalize something, but instead should have a point in order to make something illegal. The state of something for which there is no good reason to make illegal, should be legal, as otherwise it needlessly restricts freedom. Arguments based on tradition or on, "because I don't like it" have caused enough problems.
While I don't like polygamy, I would not strive to keep it illegal unless presented with very compelling reasons for doing so.
-Lyn