The essay is best read in its entirety, with all of its logical connections. However, I cannot resist quoting the passages that make Harris's central point:
[I]t is a mistake to conflate the automatic with the irrational, since, as we have seen, an automatic and mindless response is precisely the mechanism by which the visceral code speaks to us. It triggers a rush of emotions because it is designed to do precisely this. Like certain automatic reflexes, such as jerking your hand off a burning stovetop, the sheer immediacy of our visceral response, far from being proof of its irrationality, demonstrates the critical importance, in times of peril and crisis, of not thinking before we act. If a man had to think before jumping out of the way of an onrushing car, or to meditate on his options before removing his hand from that hot stovetop, then reason, rather than being our help, would become our enemy. Some decisions are better left to reflexes — be these of our neurological system or of our visceral system....Thus, in the name of "enlightenment," the "reflective class" subverts liberty.
Imagine a stranger coming up to you and asking if he can drive your eight-year-old daughter around town in his new car. Presumably, no matter how nicely the stranger asked this question, you would say no. But suppose he started to ask why you won’t let him take your little girl for a ride. What if he said, “Listen, tell you what. I’ll give her my cell phone and you can call her anytime you want”? What kind of obligation are you under to give a reason to a complete stranger for why he shouldn’t be allowed to drive off with your daughter?
None. A question that is out of order does not require or deserve an answer. The moment you begin to answer the question as if it were in order, it is too late to point out your original objection to the question in the first place, which really was: Over my dead body.
Marriage was something that, until only quite recently, seemed to be securely in the hands of married people. It was what married people had engaged in, and certainly not a special privilege that had been extended to them to the exclusion of other human beings.... Was [marriage] defined as between a man and a woman? Well, yes, but only in the sense that a cheese omelet is defined as an egg and some cheese — without the least intention of insulting either orange juice or toast by their omission from this definition. Orange juice and toast are fine things in themselves — you just can’t make an omelet out of them.
Those who are married now, and those thinking about getting married or teaching their children that they should grow up and get married, may all be perfect idiots, mindlessly parroting a message wired into them before they were old enough to know better. But they are passing on, through the uniquely reliable visceral code, the great postulate of transgenerational duty: not to beseech people to make the world a better place, but to make children whose children will leave it a better world and not merely a world with better abstract ideals....
Marriage must not be mocked or ridiculed. But can marriage keep its solemnity now? Who will tell the rising generation that there are standards they must not fail to meet if they wish to live in a way that their grandfathers could respect?
This is how those fond of abstract reasoning can destroy the ethical foundations of a society without anyone’s noticing it. They throw up for debate that which no one before ever thought about debating. They take the collective visceral code that has bound parents to grandchildren from time immemorial, in every culture known to man, and make of it a topic for fashionable intellectual chatter.
Ask yourself what is so secure about the ethical baseline of our current level of civilization that it might not be opened up for question, or what deeply cherished way of doing things will suddenly be cast in the role of a “residual personal prejudice.”
We are witnessing the triumph of a Newspeak in which those who simply wish to preserve their own way of life, to pass their core values down to their grandchildren more or less intact, no longer even have a language in which they can address their grievances. In this essay I have tried to produce the roughest sketch of what such language might look like and how it could be used to defend those values that represent what Hegel called the substantive class of community — the class that represents the ethical baseline of the society and whose ethical solidity and unimaginativeness permit the high-spirited experimentation of the reflective class to go forward without the risk of complete societal collapse.
If the reflective class, represented by intellectuals in the media and the academic world, continues to undermine the ideological superstructure of the visceral code operative among the “culturally backward,” it may eventually succeed in subverting and even destroying the visceral code that has established the common high ethical baseline of the average American — and it will have done all of this out of the insane belief that abstract maxims concerning justice and tolerance can take the place of a visceral code that is the outcome of the accumulated cultural revolution of our long human past.
Harris, by the way, has no immediate, personal interest in the preservation of marriage as a heterosexual institution. He flatly states in the essay that he is homosexual.