add what people GET for spreading rumors, and why those reasons are selfish and short sighted.
1.the illusion of popularity
2. power briefly to ruin others
3.temporary "friends" afraid of being the next victim
do that part of the speech with a lot on contempt, so the audience will realize that nothing is ever gained for long by being a rumor monger. Add that when the rumor monger is found out, they become a social outcast, which is often true.