This guys, Lucius Junius Brutus, was a hero of the republic and his killing of then king Lucius Tarquinius Superbus regarded as a great, inspiring act.
Romans according to legends swore to never have a king again. For that reason there was never a king in the empire but an emperor who was not de jure a king, he just held all the leading political functions at once :).
So these assassins who killed Caesar saw themselves as heroes, they didn't think they'll be regarded as criminals and condemned but expected to be the saviours of the republic and remembered for ages to come.
Later in the revolutionary years, when e.g. french republicans were slaying king they too looked up to the legend of the very first Brutus and saw themselves not merely assassins but heroes of the people.
In the case of the very first Brutus, they swore to kill the king after he raped and killed one of his companions wife, one can definitely argue he was a heroic figure. In the case of latter wannabe Brutuses it's very clear they aimed for power consciously or subconsciously hiding behind ideals. The subsequent genocides and thefts of property like in the case of French revolution or Lenin's who even died of syphilis are just too obvious.