If we each take the time to do exhaustive research and independent experiments to determine for ourselves whether bike helmets really work, and we do not ride until we have made up our minds, a lot of cyclists will be kept off the road while they do their homework.
If, instead, we trust experts on one side or the other, we're really taking it more on faith. But faith is the one thing we are told to suspect. Read the studies and decide for yourself! It's as simple as [insert disputed topic here].
Let me know how it turns out.