When he was twelve years old he embraced the dress of a philosopher, and later, the endurance — studying in a Greek cloak and sleeping on the ground. There is a good deal of destabilising evidence. The fact that Plato was himself a philosopher probably had a lot to do with his choice as well.
It is a very good question, especially when those guardians come armed with some big-plan ideology, a few willing henchmen, and a taste for utopian social reform.
Democracy is a word that now has positive connotations, and for good reasons. His Meaningful Name referred to his tendency to ban everyone from his court discussions who doesn't agree with him, making the whole thing an echo chamber. He overthrew the tyrant Dionysius II of Syracuse and was installed as leader in the city, only to be made to leave by the Syracusans who were unhappy with his opposition to democratic reforms.
Perhaps it is an Age of Reason, in which older, barbaric measures of manhood such as war and business have been phased out, and replaced solely with pure, unclouded Thought. He was later re-invited to the city, where he attempted to establish an aristocracy along Platonic lines, but he was assassinated by plotters in the pay of the former tyrant.
Such princes deserved the honour of restoring the republic, had the Romans of their days been capable of enjoying a rational freedom.
And how can we? It's unknown if he contributed, but he did sponsor the biblical translation that bears his name.