The innocence of the ancients did not extend to their failure to understand evil. It was their very appreciation of the power of evil and the difficulty of overcoming evil that led to our magnificent Constitution, to the Bible, and to the various re-awakenings that peppered past ages.
Liberals today are naive to the very evil that flows from their beliefs. They are deluded by a false sense of their vaunted intelligence. They are instead, dense, thick headed, small minded, weak willed, and without the desire to engage in the struggle to learn hard truths. Progressives are, in a word, dumb.
If only they were dumb!
The word you seek is "ignorant."