Why would one want to ignore beneficial knowledge received in the form of tradition? To be able to re-invent the wheel?
You want to be skeptical of tradition as a source of factual information because, while there exists beneficial knowledge that may be received in the form of tradition, it is impossible to reliably separate it from harmful false "knowledge" received in the form of tradition, without first turning it into knowledge derived from structured scientific information gathering.
Evolution/Survivability of a group usually takes care of that
Yeah, slightly harmful/long term harmful things will go though, but not major things.
Someone discovered cheese with mold is edible (probably happened in a low food situation), but there's a high likelihood on people having tried other things with mold and it didn't work out as expected.
Not washing hands survived for a very long time, and lead to huge child mortality. Humanity survived, but lots of people died for no good reason.
Lots of people may have died from avoidable diseases, but lots of people may also have avoided death by bandits, wild animals, and starvation. (due to more workers allocated to water collection than food production; the extra food produced may have been the difference between life and death during famines for some people.)
I am willing to put to test the the traditional practices that I am (or become) aware of.
http://www.slate.com/articles/health_and_science/medical_exa...
That article is perfect example - lots of cultures have fasting. We look at the fasting results and we find something interesting about how out body works. Now we have knowledge that we can build upon.