This is a major problem with lay people understanding scientists. Scientists very often speak in terms of probabilities, and are generally the least dogmatic sorts of persons. People with no background in science will often demand certainty. I've always thought this was why the excluded middle fallacy ("Either you're with us, or you're against us.") is so popular with those on the right of the political spectrum, as studies have shown over and over that the higher your education level, the more left/liberal you tend to be.