When the new rabbi came to our Classic Reform congregation thirty years ago, probably the most upsetting move he made in leading us to the mainstream was to move the congregational seder to the second night. That went down a lot harder than moving Confirmation to Shavuot instead of the nearest Sunday or making the main service of the week Friday night instead of Sunday morning.
But why dafka should Reform Jews have a seder at all on the second night? The answer--or at least one answer--is that many Reform Jews came from Orthodox or Conservative backgrounds, and two sedorim is engrained. (Just as so many of our congregations now hold services on what used to be the day after Rosh HaShanah, and is now the second day of Rosh HaShanah.)
Another answer: We used to go to seder thirty years ago at my wife's aunt and uncle's house. Uncle Lloyd conducted a reverent service, using the old gray Union Haggadah. One year we decided to hold second seder--and I was concerned that our very different approach might be interpreted as a put-down to our host of the evening before. So I began by posing the same question I've posed here--and after hearing the various hypotheses, none of which I remember, I explained that the first night was for worship, and the second night was for study. Lloyd loved it!
But whatever we do at home, when should the congregational seder of a Reform temple be held? And I have a new answer, one that I have never heard about in practice, but surely someone will step forward to tell me that your temple does it. How about the night before the first seder?
When [the rabbi at our congregation] moved the [congregational] seder twenty-nine years ago, he commented behind the scenes that a seder should be a home event, not a synagogue event--and he and his rabbinic colleagues wanted to be with their own families for "the night." But if we can move the day back, why not move it forward? Then we would be modeling for the congregants: This is what you should be doing at home tomorrow--a very different model from this is what you should have done yesterday...
I am replying to the suggestion that a seder be held the night before Pesach. I do not at all agree with this suggestion. One of the reasons to have a synagogue seder is to include those who might have no place to go otherwise. In our small synagogue, many of the people who plan the second night seder do have a first night seder with their own families. They are busy the day before preparing their own homes for Pesach and their own seders. They can then spend the first day of Passover setting up and helping with the last-minute cooking for the second night. I know of no one who would like to change this except for those who already attend two nights of seders and would love to attend the one at our small but warm synagogue.