These words are extremely important to think about and realize in terms of scientists. In terms of PhD scientists it is almost impossible to find one who is ignorant or stupid. Stupid implies that one can’t be taught, and ignorant implies that you don’t know the facts. If one is stupid, it is almost impossible to believe that one could make it through college, much less graduate school. Throughout ones under undergraduate and graduate careers, one takes courses in everything ranging from astronomy to history to literature to the biological sciences to economics. You are exposed to these intellectual endeavors and must pass examinations in their content. One can choose to forget or ignore some things they have learned, but that is a separate issue.
The next issue to consider is mistakes. Scientists are people and we do indeed make mistakes. I would even admit to saying lots of them. I am proud to say that we have set up a rather elaborate system to catch scientific mistakes. First of all, when a scientist has made a discovery he/she must write an article about what they have done, how they have done it, what results they got, and what their conclusions are. It must be submitted to a reputable journal where it is sent to one or more referees, experts in the field, to determine if mistakes have been made or something is not completely clear. Referees are other scientists who take great pride in finding something incorrect in the work of their colleagues.
Once an article is published, other scientists who are experts in the same field will then try to duplicate the results of the research. Often improvements are discovered, but sometimes errors are found. The results of the improvements and/or the errors are then published. A good example of this process is in the “discovery” of cold fusion. It was found that errors had been made in the original work.
The issue of global warming is an excellent example of this process. It is important enough that many scientists have put a significant effort into this problem. All of the reputable work has shown that human activities are a major contributor to this problem. While a few scientists have done research to prove it is not a result of human activity, their work has not survived the critical process.
Finally I will address lying. Sometimes a scientist might lie because he is just not honest with himself. There are others, particularly when a patent or money is involved, who lie for profit or fame. Because of the processes described above, the liars don’t last very long. I know of one who was a con artist who was basically lying to himself. He had a job at a prestigious university for a while, but then found himself working on something out of his garage. Lying in science just doesn’t work for very long.