They've been getting a steady diet of it since kindergarten. It's going to take a long time to undo this brainwashing.
Oddly enough, it doesn't take that long to undo the leftist brainwashing, once a person starts getting better data to think with.
What takes the longest, is for a person to come to the realization that the Democrat party and the left have not been telling them the truth.
From there, it takes some degree of courage to work up the nerve to actually examine what the "other side" has to offer.
This is the painfully slow process that most of us escapees have gone through, but it can be done. A few more escape the liberal mind control plantation every day.