They’re back! Rabble-rousing advocates of immigration restrictions are once again ruffling feathers at the Sierra Club.

With the group’s 750,000 members now voting in their annual election (polls close April 25; members go here to vote), the immigration critics are pushing a slate of four like-minded board candidates and a “yes” vote on a population ballot measure, which reads:

Shall the Sierra Club policy on immigration, adopted by the Board of Directors in 1999 and revised in 2003, be changed to recognize the need to adopt lower limits on migration to the United States?

In the “yes” corner, Sierrans for U.S. Population Stabilization represents the views of insurgents, the most vocal of whom is current Sierra Club board member Paul Watson, founder of the Sea Shepherd Conservation Society. Their argument in a nutshell: Americans are the world’s most gluttonous consumers, and when new folks migrate to the U.S., they ramp up their gluttony to fit right in. “Our population is already too large to be sustainable within our resource base,” said club member Dick Schneider, who wrote the ballot argument in favor [PDF] of immigration limits. “Unless the U.S. population is stabilized and eventually reduced, the Sierra Club will fail in its mission.”

In the “no” corner, Groundswell Sierra represents virtually the whole Sierra Club leadership and establishment, including most board members and past presidents. (Even MoveOn.org has jumped on board with a March 18 email alert melodramatically entitled “Save the Sierra Club from Hostile Takeover.”) Their argument in a nutshell: Getting mixed up in immigration politics will alienate potential allies such as civil-rights groups, minority communities, and labor unions, and won’t do anything to solve the global population problem. “We believe population growth has to be addressed by addressing its root causes,” said former Sierra Club President Robert Cox, who wrote the ballot argument against [PDF] a change in immigration policy. “Immigration control has done nothing to reduce family size or population pressures. It just scapegoats people who end up bearing the brunt of our trade policies and foreign policy.”

It’s all exactly what you heard last year, only this time ’round the volume is lower and the insurgents are even more likely to get thoroughly crushed. Is that as it should be? Maybe. The recurring question has become a squeaky hobbyhorse for the annoying and impolitic “yes” crew, stirring up vitriol but little substantive discussion.

And that’s a shame, because it’s an issue deserving of real dialogue. Mainstream environmental groups in the U.S. avoid the topic of population like the plague, and the more volatile sub-topic of immigration like the Marburg virus. But every environmental problem is exacerbated by growing population numbers. And if the U.S. is to have any limits on immigration, isn’t concern for the nation’s environment as valid a reason for those limits as any other? (Bill McKibben dared to raise related questions in the pages of Grist last year.)

I’m conflicted over these issues myself, and for that very reason I wish the environmental community could grow up and have an open, honest, tough, fair discussion about them. But I’m not holding my breath.