When I say "any competent philosopher", I'm being specific to the Western philosophical tradition. Up through the 19th century, any education in philosophy, cl

When I say "any competent philosopher", I'm being specific to the Western philosophical tradition. Up through the 19th century, any education in philosophy, classics, or the humanities was virtually certain to include reading Plato; since then, more organized philosophy degrees in university always have some ancient philosophy requirement that includes Plato/Aristotle. Additionally, Plato is frequently used as introductory material in philosophy classes to demonstrate how it works via the Socratic method. Within the confines of "professional" philosophy today, it's almost impossible not to have a basic grasp of Plato. As for how and why we think differently today: any study of the history of philosophy is partly the study of refuting earlier philosophers. If you're aware of Plato, you're aware of criticisms of Plato and how that formed the basis of other ideas.