Do we really need to discuss this again?
Sigh... If someone is for some reason interested in my take and missed my previous posts, I think it's not inherently unacceptable, but (from what I've heard of it) is often practiced in ways that entail other morally unacceptable attitudes.
A lot of things are like that.
I think I'm in agreement with Anthony here in that, while I don't think it's inherently unacceptable, in practice it seems very difficult to ensure an equitable division of power in such a relationship, and to ensure that no one is abused. But as long as abuse isn't happening, well, I'm a stalwart believer that two consenting adults should be able to do whatever the hell they want.
The highest ethical principle here is each person's entitlement to their space.
My take on it is that it might be good to experiment with but I don't think it is a way to live your entire life like. Then again, I was pretty homophobic when I was like 16 and this is where I evolved to when I was like 17 or 18 on homosexuality and by the time I was 19, I was totally fine with it so who knows? But this has been my view on polyamoury for the last 5 years so maybe I won't evolve on the issue.