It's a very established term in that community.

If you want to pick on a word for technical reasons, 'polyamory' itself is actually pretty popular. I can't find a link to the quote now, but it was something along the lines of "Half greek, and half latin? Obviously wrong."

E.g. http://www.zazzle.com/polyamory_is_wrong_tshirt-235470507350.... Yes, it's a stupid term, but it's established at this point...