We all know that the debate about vaccines is contentious. In general, mixing science and emotion is a dangerous laboratory experiment. However, the controversy took an interesting turn the other day when AMC Entertainment, which runs the AMC movie theater chain, did a last-minute about-face and chose not to run a 30-second ad from a non-profit that warns against the use of mercury in flu vaccines.

Here’s the short of it: The Coalition for Safe Minds, which says it is not an anti-vaccine group, produced what it calls a public service announcement (see above) that tells viewers mercury is a dangerous toxin and the public should demand mercury-free flu shots. “The PSA alerts parents and pregnant women of the presence of mercury in most influenza vaccines and the ample availability of mercury-free alternatives. The CDC has declined to give a preference for the mercury-free versions, so it is important that the public is aware of its options,” a Safe Minds spokeswoman writes us.

More than a decade ago, public health agencies and vaccine makers agreed to reduce or eliminate its use, although the Centers for Disease Control & Prevention notes there are no proven safety issues at low doses and mercury is not linked to autism, which remains at the heart of the long-running row (you can read more here).

And so a different sort of backlash began when Skepchick generated an Internet outcry that Safe Minds was using junk science. That prompted AMC to change its corporate mind and decide against running the Safe Minds ad. “We have not and will not run any ads about that topic,” a spokesman writes us, using language that tries to appease both sides. “It’s a worthy debate and should be discussed. However, our theatres are not the appropriate forum for that discussion.”

This is reminiscent of the recent squabble between Breast Cancer Action, another advocacy group, and billboard companies over a campaign to publicize a possible link between cancer and recombinant bovine growth hormone, or rBGH, which is sold in products made by Eli Lilly’s animal health unit (look here). In both cases, non-profits with critical messages ran up against companies that exercised their right to decline an ad. Such moves, however, will not stop the debates. That is one fact that we can confidently advertise ourselves.