Chakma613, I'm sorry to tell you this but you are mistaken. First of all, polygamy is NOT wrong, the Torah allows polygamy and whatever the Torah allows is permitted. Rabbis are NOT allowed to make decrees forbidding something the Torah permits, as the Torah says "do not add to it and do not take away from it" with the one exception of a Horah Shah or in English an emergency temporary decree lasting a very short time. This is why Rabbenu Gershom's decree is controversial, since he made a 1000 year decree, which JDL4EVER and the Sephardic Jews think that this is not allowed for a Rabbi to do, since a Horah Shah is only supposed to be a for a very short time period of imminent like at most for lasting a few years. The second mystery is why Rabbenu Gershom made this decree. You give an explanation that the Jews weren't practicing polygamy properly which makes no sense at all to me, there is no proper way at all to practice polygamy if it is a permitted practice. In my opinion, the real explanation is that he didn't want the Gentiles living with us to make fun of us for having several wives when they don't practice polygamy any more, so he made this decree. Obviously, if this was the reason for his decree "to not offend the Gentiles", then we can understand why the Sephardic Jews didn't accept this decree since this is not a reason of imminent need, as R' Kahane would say "who cares about what the Gentiles think, we follow the Torah". Thirdly, his 1000 year decree expired already so polygamy is no longer forbidden for Askenazim, but none the less we don't do it any more since it hasn't been practiced for 1000 years. The Sephardic Jews recently used to practice polygamy. My father's Karate instructor was a Sephardic Jew from an Arab country who's father had 2 wives.
You have to be careful to not add anything to the Torah like making up stories that when polygamy was used to only allowed if you marry orphans. I know your intentions are for the sake of heaven, but you are adding to the Torah, which is forbidden. The Torah allows polygamy and does not add any rules to it with the exception on the limit on the number of wives you could have.