"I doubt whether many slaves, once they hear of this, will rise against Rome in the future"
The ancient Romans kept such a vast number of slaves and used slave labour in so many aspects of life that they were extremely vulnerable to slave revolt. This is why any rebellious slaves had to be punished severely and publicly as an example to the rest. One law stated that if a master was killed by one of his slaves, the entire household of slaves would be immediately put to death regardless of their involvement in the crime. This was intended to encourage loyalty; any slave who heard whispers of rebellion amongst the others would not wish to hold this information back from his or her master. This is why the slaves who followed Spartacus were treated so ruthlessly.