In many ways, Plato and Hobbes couldn’t be more different. Plato was an idealist, and Hobbes was a materialist. Plato advocated free will, and Hobbes was a determinist. And, famously, Plato believed in the Forms, whereas Hobbes was a staunch nominalist. But despite their differences elsewhere, the political philosophies of Plato and Hobbes are strikingly similar.
Plato advocated a dictatorship ruled by philosophers, on the grounds that philosophers alone have cognitive access to the Form of the Good. If a philosopher is given intensive training and education over the course of decades, he will be able to pierce the veil of perception and see what is really good. And once he has mystic insight into what is good, there is no reason why he shouldn’t use force to get any misguided citizens of the Republic who disagree to obey him.
Hobbes’ dictatorship was not ruled by mystics, like Plato’s. Instead, Hobbes, claiming to be an advocate of science, advocated a dictatorship run by arbitrary whim. Words like “good” and “justice” are controversial, and there is no objective way to settle disputes about these ideas, since they are subjective. So, according to Hobbes, everyone should submit to an all powerful Leviathan out of fear of anarchy, and just agree to treat the ruler as right by definition.
Why did Plato and Hobbes both end up advocating tyranny, even though they disagreed on so many points? The answer is that, although they might superficially look like opposites, mysticism and subjectivism can both lead to tyranny in practice. Mysticism can lead to a dictatorship ruled by mystics, whereas subjectivism can lead to a dictatorship ruled by the feelings of the dictator.