'But then, when you're not accustomed to history, most facts about the past sound incredible'

History is not taught in the 'Brave New World'. This makes people incredibly easy to manipulate, as tradition is something that is hard to forget.

They simply use people as a blank slate to imprint information on.Without knowledge of history, these people don't know what they're missing.

 

'For a very long period before the time of Our Ford, and even for some generations afterwards, erotic play between children had been regarded as abnormal; and not only abnormal, actually immoral: and had therefore been rigorously suppressed.'

This quote shows how fast mentality over a subject can change, if a person has no tradition regarding said subject. If people are taught that erotic play between children is perfectly normal, and everyone around you says it too, you have very little reason to be disgusted by the act.

 

'You all remember, I suppose, that beautiful and inspired saying of Our Ford's: History is bunk. '

The reason people are taught this, is to make them more compliant to the civilisation and society in Brave New World. They don't know what they're missing. 

 

These," he said gravely, "are unpleasant facts; I know it. But then most historical facts are unpleasant.

Huxley grew up in a time where history did not have the same centre place, compared to today. The historical facts were about the first World War, which wasn't exactly pleasant to think about, and some sparse times before that.

 

'Murder kills only the individual—and, after all, what is an individual?" With a sweeping gesture he indicated the rows of microscopes, the test-tubes, the incubators. "We can make a new one with the greatest ease—as many as we like. Unorthodoxy threatens more than the life of a mere individual; it strikes at Society itself.'

This can be compared as to how human life was treated in the first World War. People only cared about the results, but the millions upon millions of people who died were kept hushed.There was very little respect for the individual lives of each person who fought in the army.