One of the most surprising things I’ve witnessed in my lifetime is the rebirth of the concept of heresy.
In his excellent biography of Newton, Richard Westfall writes about the moment when he was elected a fellow of Trinity College:
Supported comfortably, Newton was free to devote himself wholly to whatever he chose. To remain on, he had only to avoid the three unforgivable sins: crime, heresy, and marriage. 
The first time I read that, in the 1990s, it sounded amusingly medieval. How strange, to have to avoid committing heresy.
But when I reread it 20 years later it sounded like a description of contemporary employment.There are an ever-increasing number of opinions you can be fired for. Those doing the firing don’t use the word “heresy” to describe them, but structurally they’re equivalent.
Structurally there are two distinctive things about heresy:
(1) that it takes priority over the question of truth or falsity, and
(2) that it outweighs everything else the speaker has done.
For example, when someone calls a statement “x-ist,” they’re also implicitly saying that this is the end of the discussion.
They do not, having said this, go on to consider whether the statement is true or not.
Using such labels is the conversational equivalent of signalling an exception. That’s one of the reasons they’re used: to end a discussion.
If you find yourself talking to someone who uses these labels a lot, it might be worthwhile to ask them explicitly if they believe any babies are being thrown out with the bathwater.
Can a statement be x-ist, for whatever value of x, and also true?
If the answer is yes, then they’re admitting to banning the truth. That’s obvious enough that I’d guess most would answer no.
But if they answer no, it’s easy to show that they’re mistaken, and that in practice such labels are applied to statements regardless of their truth or falsity.The clearest evidence of this is that whether a statement is considered x-ist often depends on who said it.
Truth doesn’t work that way.
The same statement can’t be true when one person says it, but x-ist, and therefore false, when another person does. 
The other distinctive thing about heresies, compared to ordinary opinions, is that the public expression of them outweighs everything else the speaker has done.
In ordinary matters, like knowledge of history, or taste in music, you’re judged by the average of your opinions.
A heresy is qualitatively different. It’s like dropping a chunk of uranium onto the scale.
Back in the day (and still, in some places) the punishment for heresy was death. You could have led a life of exemplary goodness, but if you publicly doubted, say, the divinity of Christ, you were going to burn.
Nowadays, in civilized countries, heretics only get fired in the metaphorical sense, by losing their jobs. But the structure of the situation is the same: the heresy outweighs everything else.
You could have spent the last ten years saving children’s lives, but if you express certain opinions, you’re automatically fired.
It’s much the same as if you committed a crime. No matter how virtuously you’ve lived, if you commit a crime, you must still suffer the penalty of the law.
Having lived a previously blameless life might mitigate the punishment, but it doesn’t affect whether you’re guilty or not.
A heresy is an opinion whose expression is treated like a crime — one that makes some people feel not merely that you’re mistaken, but that you should be punished.
Indeed, their desire to see you punished is often stronger than it would be if you’d committed an actual crime.
There are many on the far left who believe strongly in the reintegration of felons (as I do myself), and yet seem to feel that anyone guilty of certain heresies should never work again.
There are always some heresies — some opinions you’d be punished for expressing. But there are a lot more now than there were a few decades ago, and even those who are happy about this would have to agree that it’s so.
Why has this antiquated-sounding religious concept come back in a secular form?
And why now?