Media was a smaller community then - three television networks, and for national stories local reporters rewrote wire pieces from a centralized pool. If you had a few journalists as allies you had a large chunk of public thinking in your grasp, and breast cancer had a lot more sympathy than something like cirrhosis. CSPI did what activists do, they found a study that used raging binge drinkers and extrapolated that out to everyone, and then boosted their claims by citing every pooled analysis of cohort studies (.e.g. JAMA. 1998;279:535-540) - the kind of epidemiological data dredging Harvard School of Public Health publishes every month - they could find.
They have long traded in an ''attitude of crisis'' mentality, and their tools are 'health sensationalism' and half-truths. The founder, Michael Jacobson, was a thug when it came to scientists, and an overt sexist on top of it. His foal was to find companies to sue, that provided the bulk of their revenue, and they could claim victories in meaningless gestures like getting a sulfite warning on wine.
There is no known maximum safe level of alcohol, human biology is too variable to create one, but groups like CSPI weaponized the language of science and spun that to mean no level of alcohol is safe - as in "there is no safe level of alcohol." Which is false, even in pregnant women. Europe does not have American Puritanism about a glass of wine during pregnancy and they don't have any more birth defects than America has. Yet women are shamed and told they should be abstinence only because a study in the 1970s got famous for its analysis of a few hundred binge-drinking alcoholics who did give birth to more babies with birth defects.
Alcohol is a class 1 carcinogen, the Interntional Agency for Research on Cancer made that ruling long before they were hijacked by environmental consultants such as Chris Portier, Martyn Smith, or anyone Linda Birnbaum at National Institute of Environmental Health Sciences (NIEHS) is willing to hire. But that is at high doses. Plenty of people who got throat cancer also drank alcohol. A few even smoked cigars. Those can be statistically linked, but not scientifically, unless someone consumed vast quantities of those throat and mouth irritatants.
Their claims about breast cancer and alcohol fizzled out after a while, their desired outcome, a class action lawsuit against Big Alcohol where the cy pres award just happens to go to CSPI, never happened. But prior to that plenty of epidemiologists saw media buzz about it and armed with mouse studies and statistical correlation started producing papers. A culture where activists have been so successful in their war on science a jury can be convinced that a weedkiller which only acts on a pathway in plants, or that baby powder causes cervical cancer, couldn't produce a mass uprising against alcohol. Instead, statistics and mouse studies could even show it was beneficial, and a whole field of woo grew up around that.
Like a low-fat diet being the rage among Baby Boomers, there are a number of people who still believe alcohol causes breast cancer - including the U.K. National Health System.