Do not believe ....

Many of those people would be better off if they didn't believe in a lot of that stuff.

Do not believe in anything simply because you have heard it. Do not believe in anything simply because it is spoken and rumored by many. Do not believe in anything simply because it is found written in your religious books. Do not believe in anything merely on the authority of your teachers and elders. Do not believe in traditions because they have been handed down for many generations. But after observation and analysis, when you find that anything agrees with reason and is conducive to the good and benefit of one and all, then accept it and live up to it.

Buddha (Kalama Sutra; From Joe Cherry's quotes page)

But compare this version:

Do not go upon what has been acquired by repeated hearing; nor upon tradition; nor upon rumor; nor upon what is in a scripture; nor upon surmise; nor upon an axiom; nor upon specious reasoning; nor upon a bias towards a notion that has been pondered over; nor upon another's seeming ability; nor upon the consideration, 'The monk is our teacher.'...[W]hen you yourselves know: 'These things are good; these things are not blamable; these things are praised by the wise; undertaken and observed, these things lead to benefit and happiness,' enter on and abide in them.

It's also identified as being from the Kesamutti Sutta, the fifth sutta (sutra) in the Book of Threes (Mahavagga) in the Gradual Sayings (Tika Nipata). There apparently is no standard Chinese version, although I found references to 伽蓝经.

Anyway, shades of Carl Sagan's Baloney Detection Kit.