Perhaps the idol is unity. I believe you can find a few references in the Bible to not associating with those who call themselves believers and choose to persist in a pattern of sinful behavior.
And perhaps there is a total lack of clarity concerning the prioritization(s) of ecumenical efforts by the ELCA.
First should be intra-Lutheran unity with the LC-MS. Extremists on both sides have made that a total non-possibility; the ready embrace and disproportionate influence of the AELC/Seminex schismatics will be neither forgotten nor forgiven by St. Louis.
Second should be serving as a bridge church between the Eastern Patriarch and the Bishop of Rome; but the extremist embrace of abortion, gay rights, etc, have rendered that also a non-possibility.
So the only remaining course is to become part of generic American liberal Protestantism. Never mind that it was tried and failed by Samuel Simon Schmucker et. al. in the mid 19th Century.
"Those who do not learn from history...."