That's an interesting point. For most beliefs, they are pretty long held and tend to move slowly (morality), but it's interesting to consider how science changes and what people's thoughts on that are, and recent quick changes in beliefs.

Example, diet fads, or what new thing causes or prevents cancer (red wine/chocolate/low carb/high carb). Some people really strongly hold these beliefs, and they do get moved around when new beliefs come out. To their detriment, usually (especially with diet fads).

I'd rather have someone have a strongly questioned strong belief, a weakly held weak belief, and the ability to know that just because you believe something doesn't make it exist.