He likely knew it was a dumb idea from the beginning. At the end of his life, it looks like he changed his mind, became more practical. Or maybe it was Socrates who was the foolish idealist; maybe it’s the mature Plato we discover in his later writings, certainly a more sensible Plato.
It should be required reading, I think, for members of the clergy: Nathaniel Hawthorne’s The Scarlet Letter, that masterpiece of American literature and of the American psyche.