“Eat the Meat and Spit Out the Bones”... is this a good way to view bad teaching?

Is it OK to tolerate false teaching as long as there is some good teaching in there too?

“Eat the Meat and Spit Out the Bones” is popular phrase used when people question a false teaching or an error. The phrase is a plea to allow the mixture of truth and error (good with the bad), just because some truth or good is present. Maybe it is feared that removing the bad would somehow stop the good… so the mixture of the two is encouraged (in other words, “don't throw the baby out with the bath water”).

The following scripture is often quoted to support this: 1 Thessalonians 5:19-21 Do not quench the Spirit. Do not despise prophecies. Test all things; hold fast what is good. (Notice what is not quoted - the very next verse). 22  Abstain from every form of evil..

How are we to avoid evil if we are encouraged to accept the mixture? 

It is like taking a nice clean glass of water and adding a few drops of cyanide…Would you drink the water?

I suppose some people have never read: a little leaven leavens the whole lump (Gal. 5:9).