It's not an opinion, it's a fact. Plato uses that very geographic landmark in his text. And Herodotus also refers to the Pillars of Hercules in such a way that it can only refer to Gibraltar -- and so do all other ancient sources which mention the Pillars of Hercules. Saying that Plato's "Pillars of Hercules" refers to some place off SE Asia is a matter of opinion. :')