Those who were never in the belly of the beast could not possibly understand. They can only comment in the abstract. They are clueless as to the real danger the hardcore Left presents.
I know I can't. I have met some... I have had conversations and 'debates' with hard core leftists a few times which went totally circular until they inevitably exploded in rage and resorted to the typical ad hominem attacks. But you are correct. I only really know them in the abstract.
I read Horowitz's Radical Son a number of years ago and found it profound in that it gave me a fair idea just how ugly the belly of the American leftist beast is.