I don't want to get too technical with this, but it might help to borrow from moral psychology. One school has it that there are three broad "schemas" of moral judgment:
1. Pre-conventional, which is all about avoiding punishment. (An act is wrong if I will get in trouble for it.)
2. Conventional, which is all about upholding social norms for their own sake. (An act is wrong if it violates the explicit, agreed-upon rules or standards of society.)
3. Post-conventional, which is all about independent judgment based on higher ethical principles, which makes it possible to critique social norms . . . and to give reasons for it.
Now, there are several different frameworks for post-conventional moral thinking, which means multiple distinct lines of argument that can be made. The problem is that it can be very difficult to argue with someone whose moral thinking is dominated by the conventional schema.
So, from a conventional point of view, here in Western culture, lifelong, exclusive monogamous marriage is a social norm, surrounded by expectations and social sanctions. For someone whose thinking is dominated by the convention schema, monogamy is simply right, and any departure from it is wrong almost by definition.
There are several lines of argument that can be made in favor of non-monogamy or, at least, in favor of allowing people to choose. How well the arguments are received depends on how open the other person is to reconsidering social norms, seeing new possibilities. It depends how much moral imagination the other person has.
I sometimes think that's why so many people who consider themselves poly are also science fiction fans: at its best, sf can reveal an astonishing array of alternative ways of living in the world, so readers and viewers of sf may may be more likely than others to imagine other ways of living their own lives.
Anyway, one framework would focus on happiness and the avoidance of harm. If polyamory makes it possible for someone to live a full and happy life, and if it's practiced so as to avoid harming others as much as possible, then it may be morally justifiable.
Another framework would focus on character and the development of virtues. I think being poly has made me a better kind of person, in some respects. I am more honest with myself and others, living more deliberately in the world. I'm more mature than I was. This is not to say people practicing monogamy can't be honest and mature, but it's worth considering whether the demands of compulsory monogamy would tend to stunt that particular line of development.
For me, the most compelling framework would focus on consent and respect for the free choice others. As long as I am not using other people merely as means to my own ends, as long as I allow others to make their own decisions, without any attempt to coerse or deceive or otherwise control them, as long as my relationships are based on honesty, trust, respect, and mutual consent, then my way of relating to others is moral.
I've told the story in other contexts, but it's relevant here in that it simplifies all of this, boils it down to its essence.
Vix and I moved in together before we were married, which shocked and horrified my parents. It went against what my Dad still calls "the Program.". They are very much conventional thinkers, defining right and wrong entirely in terms of conformity to social norms and expectations. So, from their point of view, having sex outside of a committed, lifelong, heterosexual marriage is and always must be immoral.
When I told my parents the reason for my change of address, my mother cried. She demanded to know: "Where's the moral young man we've raised?"
I replied along these lines: "I'm right here! It's just have a different understanding of what it means to be moral. I have made my choice, consciously and thoughtfully, and I take responsibility for my choice and its consequences."
They were unconvinced, and probably unconvinceable.
But that's what I think it comes down to: making choices, thoughtfully and responsibly.
"Ignorance more frequently begets confidence than does knowledge" - Charles Darwin
"Mystical explanations are considered deep. The truth is that they are not even superficial." - Friedrich Nietzsche
Last edited by hyperskeptic; 06-25-2012 at 12:38 PM.