Rashi comments: There was no water in the pit, but there were serpents and scorpions in it. Horav Elyakim Schlessinger, Shlita explains the halachic ramifications that vary between a pit filled with water and one filled with poisonous serpents and scorpions. It was Reuven who suggested that rather than take action outright against Yosef, they should put him into a pit. Had there been water in the pit, it would not be a direct act of murder. Throwing Yosef into a pit filled with poisonous creatures, however, is no different than tying a person up and placing him in front of a lion, which the Rambam rules is active murder. In any event, Yosef was going to die.
Rav Schlessinger explains that the brothers were certain that Yosef’s righteousness would protect him from the poisonous creatures. This is consistent with Ramban’s opinion (Parshas Bechukosai) that animals can strike a human being only if he is tainted by sin. A tzaddik, righteous person, reigns over animals. The brothers were well aware that Yosef was without sin. Thus, even though serpents and scorpions were in the pit, the brothers would not be halachically liable for active murder. What about Yosef starving to death? Ramban posits that causing starvation is also not considered active murder. Thus, it is not punishable by a Bais Din, Jewish Court of Law.
A powerful, frightening lesson can be derived from this. Although they knew that Yosef was a tzaddik who had no sin, they nonetheless ruled that he was a rodef, pursuer, who was liable for the death penalty. Why? He was misguided in his belief and, thus, harmful to the future of Klal Yisrael. If one’s shitah, ideology/judgment, opinion is flawed, misguided, then he presents a grave danger to his followers – especially if he is righteous. At times, innocence and naiveté can sully one’s outlook in such a manner that it catalyzes harmful decisions.