Why did Paul's heart sink when he looked at Athens?

Les explains that after Paul left Berea, he came down the coast to southern Greece and arrived at Athens, which was the very seat of culture in those days. The Parthenon stood on the Acropolis, and halfway up the Acropolis was Mars Hill. On the path up to the Acropolis were idols of all their various gods and goddesses. Les imagines Paul standing there and looking out over that pagan city, and his heart just sank because the whole city was steeped in idolatry. Even though Paul had seen idolatry everywhere he had been, it was especially grievous that this seat of learning, with intellectual people, followed such false religion. Les notes that many wonder how intelligent, reading people can follow such drivel, but they were doing it there as well.