Scientific method serves to develop progressively more accurate theories by testing hypotheses and discarding those that do not stand up to scrutiny. It "changes opinion" because while scientific understanding is influenced by intellectual trends, cultural dogma, political pressure to manufacture evidence, etc., its fundamental emphasis on testing works as a corrective force in the long run. (As Kuhn noted in _The Structure of Scientific Revolutions_, if the old generation refuses to let go of old models a generation may pass before new ideas are really accepted, but such change can be measured in years rather than millennia.)

It's rare for Science to form an opinion let alone for it to change it's opinion. You often hear single study's saying something, but Science only cares about what has been independently verified by several studies. The media presents controversy even with tiny fraction's of the community so that you listen. A classic case in point is "String Theory" which people compare to the "Standard Model" but it's still just an area of research that does not have the acceptance of the community of large.

A far more important case is the effects of low levels of radiation on cancer. It's been assumed my some people that there is a linear relationship between the risk of cancer and total radiation but there is still a lot of debate on the topic.

In both cased their are competing ideas, but the entrenched idea is just older and unlike evolution or the general theory of relativity it's far from accepted as correct.