The problem is that the true definition of the left is "the ideology of cancer" - whatever it takes to grow and gain power
But if you define the left correctly then you can't have a polite conversation with the left - you can only offer them the choice of abandoning it or get 
Trying to defend "the Enlightenment" or "classical liberalism" is a pathetic defense of something that isn't even an ideology - just an earlier stage "I'm in favor of stage 1 cancer, ya know, before it spreads to the brain" isn't a viable position