This may be the book of the decade, hopefully in the sense that it sells a lot, but at least in the sense that it explains so much behavior distinctive or amplified by our social media-fueled decade.
That said, the phenomenon it describes is old. Indeed, Jesus complains about it in Matthew 6:5:
And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by others.
The point is that such people are less concerned with connecting with God and more concerned with inducing other people to believe the they are good and pious.
"Moral grandstanding" refers to when people use moral language for self-promotion. As Warmke explains in an interview, "Grandstanders are moral show boaters who use public discourse as a vanity project. They aren't really concerned about helping people or contributing to a conversation."
When people engage in moral grandstanding, they are trying to raise their own status and prestige through the use of moral language. They are trying to get others to think more highly of them or to secure various benefits for themselves.
Some example forms of grandstanding include:
1. Ramping Up: Making increasingly strong claims about the matter under discussion. Engaging in a kind of moral arms race. (E.g., "Washington was a racist slave owner." "Oh, yeah, well, he was also sexist and heteronormative too. I guess you didn't see that."). Here, people are trying to show off their moral purity and moral sensitivity by making increasingly strong claims.
2. Trumping Up: Insisting on the existence of a moral problem where there isn't one, or exaggerating a problem dramatically. Think of the story of the princess and the pea. A real princess is so sensitive that she can feel the presence of a pea under 40 mattresses. Well, some people like to show off heir moral sensitivity by finding moral problems everywhere, and then announcing their distaste and shaming others for not also finding those problems. Again, the point is to raise their own status.
3. Dismissiveness: Insisting that one's own point of view is obvious and that any disagreement is obviously stupid and vile. Here, the person is trying to signal their virtue and moral purity by being unwilling to interact with contrary points of view. You can see a great deal of this in contemporary philosophy about race and gender issues, where many of the theorists act like the controversial stuff they are saying--stuff they didn't themselves believe 3 years ago--is obviously true, and that it's beyond the pale to acknowledge or debate anyone who disagrees. "I'm such a good person I can't even tolerate reading what others say."
4. Excessive emotional displays: People go out of their way to emote in reaction to things, often in disproportionate ways. Go on Facebook today and you'll surely see some of this: You'll see friends crying and whining about bad news, acting like it destroys them. I have academic friends who brag--yes, "brag" is the right word--about how Trump's election bothered them so much that they couldn't get any writing done for six months. Here, the goal is to signal, "I'm such a morally sensitive and good person that I can't even handle the news. Oh, you kept going about your life like normal? I guess you aren't as good as I am."
The book identifies how grandstanding works, explains what makes it morally wrong, diagnoses a great deal of social and political behavior, and finally ends with recommendations about what to do about it. In particular, they recommend against trying to police others' moral grandstanding (you'll probably just engage in grandstanding yourself when you do) and instead policing yourself.
Tosi and Warmke are now working with psychologists to run experiments testing various empirical hypotheses about grandstanding. While these papers came after the book was written, to be clear, it is a demonstrably real phenomenon. Their psychological work is able to show that people are often using moral language for self-promotion rather than for other reasons.
If you don't buy and read this book today, you must not care about ethics.