All good man will one day fall.. He was too much of a people leader, gaining too much power which could corrupt him so they decided to just prevent that. Everyone, even today, who changes the world, will soon fall too.. or something like that..
The point is that people are jealous and they just don't want one person holding all the power, either good or bad. They were wrong on killing him just because of power, but if they could prove that somehow, Julius will abuse his power, then it was right to kill him to prevent it.
''Nearly all men can stand adversity, but if you want to test a man's character, give him power.'' ~Abraham Lincoln~