This is not what Farah was saying. He said that libertarians do not understand that man is inherently bad. Which has a lot of truth to it.
Some people are bad, some are good. Some are bad one day and good the next. Some are good in one area of their lives and bad in others. Being overly general and stating that man is either totaly good or evil in nature is very simplistic, and idealistic. Something he accuses libertarians of.
I don't think he is saying that he thinks man is inherently bad. I admit am puzzled why he thinks libertarians believe man is inherently good? I think libertarians are far more realistic than he believes.