Okay, folks, here's my rationale. And, in the interests of full disclosure, I'll admit here that I do have a small soft spot for Ralph since I voted for him in 1996 in our school poll. He finished a distant second, but still doubled Bob Dole's vote (who finished behind Ross Perot as well)
Anyway, nobody who's willing to cast their vote for Ralph in 2004 would even consider voting for the Democratic candidate. Not holding their nose and voting, not nothing. We had a graphic demonstration of what it means to vote for a third party in a close election back in 2000, so people who are even vaguely ABB won't go Ralph's way. They'd either have voted for the new Green candidate or have stayed home. People who voted for Nader over Gore learned their lesson, and I don't think we could realistically get the votes of too many people who vote for Nader over Kerry(or Edwards)
Furthermore, the Greens don't run somebody for every election, and with Ralph bringing only liberals (and leftists) into the race, it means more votes for our downticket candidates, particularly local figures who the voter may have a more personal stake in seeing out of office.
Additionally, Ralph's campaign will cut the influence of the actual Green party, and help keep them out of elections in the future, when the mission to beat the Republican won't quite be so clear. Nobody will get their matching-funds 5% with the leftist vote split, so that'll help us out.
Finally, long term, Ralph will bring more voters into the process who at least generally agree with us. We might not be able to count on them this year, but it will mean that they'll educate themselves on the Democrats and Republicans, and with luck, it'll give us just a few extra votes in 2006 and beyond.