Why was Paul's heart troubled when he came to Athens?

Les explains that after Paul left Berea and came down to Athens, he was at the very seat of culture in those days. The Parthenon stood on the Acropolis, and halfway up was Mars Hill. Les pictures Paul standing there, looking out over that pagan city, where on the path up to the Acropolis were all the idols of their various gods and goddesses. Les says Paul's heart just sank because the whole city was steeped in idolatry, even though he had seen it everywhere he had been. What struck him was that this seat of learning, with intellectual people, was following such false religion. Les notes that many wonder the same thing: how can intelligent people who can read follow such things and believe such drivel? Yet they were doing it there as well.