On issues from genetically modified crops to climate change, scientists are confronted by critics seemingly willing to say or do anything to win the debate. Faced with such opposition, it can be tempting to push facts harder than they can bear, simply to get a hearing.

This temptation has long worried some of the scientists at the sharp end of such controversies. When the issue of global warming first made headlines in the late 1980s, the influential climate researcher Stephen Schneider expressed the hope that scientists could strike a balance "between being effective and being honest".

Yet such hope seems increasingly forlorn in one such controversy: the justifiability of animal experiments. Provoked by opponents prepared to use everything from celebrity endorsement to lethal force, the science community has begun sliding down to a slippery slope—making assertions that lack any basis in fact.

Let's be clear: Animal experiments have undoubtedly been important in many areas of medicine, from immunology to surgery. Concern over the public's lack of appreciation of this fact prompted many eminent researchers, including six Nobel prizewinners, to sign a declaration in 1990 stating that animal experiments have made "an important contribution" to medical science and surgery.

Since then, attitudes on both sides have hardened. The protests have grown more strident—and so have the pronouncements of scientists. Those same eminent researchers and even the Royal Society have taken to making a far stronger statement about the value of animal experiments: that "virtually every medical achievement of the last century has depended directly or indirectly (on research involving animals)".