Walter,

There was a time when people knew that the body was regulated by a number of humors. The sky was a big dome with holes in it. Galileo knew that tides are caused by the earth's rotation about its axis and about the sun. Malaria was so named because it was caused by evil substances propagated through air. Eggs are not/are/are not/are/are not/are/are not good for you. Red wine is/is not/is/is not good for you. Certain dysplasias always/sometimes/rarely/sometimes/rarely progress to cancer. Screening does/does not/does/does not result in better community outcomes. And so it goes on to this day: in so many areas of science, the more you know, the more you realize you don't know. The "trick" is to disincentivize those who insist they have a monopoly on truth and try to stifle dissent, especially if they do that by personally attacking those who disagree. Systematic use of terms like "deniers" ought to call into question the credibility of those who rely on the tactic: if you're so sure of yourself it's easier to attack the point, not the man.