"Virtue itself turns vice, being misapplied"

In Act II, scene iii of Romeo and Juliet, Friar Laurence talks about how Nature's creations can been used for good and for evil. He picks up a flower and notes that if he smells it, the substance has medicinal effects, but if the flower is eaten raw, it is poisonous. This is your topic. Discuss objects or substances which can be used for both good and evil.