Cato the Younger
When Cicero discovered a plot against the consuls and other magistrates in Rome, he arrested the conspirators. Cicero proposed to execute them without trial, which would have been legal under the senatus consultum ultimum. In the Senate's discussion, Julius Caesar agreed the conspirators were guilty, but argued for distributing them among Italian cities "for safekeeping". In contrast, Cato argued that capital punishment was necessary to deter treason: it was folly to wait for the test of the conspirators' guilt. Convinced by Cato's argument, the Senate approved Cicero's proposal, and  the conspirators were executed. Most of Catilina's army quit the field, much as Cato had predicted.