In the Parables of the Wheat and the Tares, the Mustard Seed, and the Leaven, Jesus was speaking to the physical nation, which the parables clearly reflect.
Before the flood, Satan had attempted to corrupt mankind, probably through massive demonic possession. The same demonic threat will occur at the end-time.
We should not expect brethren to be perfect; we all sin. God has not given His People the prerogative to judge another member as a tare.