Milo Yiannopoulos — the infamous internet troll, Donald J. Trump supporter and editor at Breitbart News — has compared Islam to cancer, mocked transgender people and suggested that women who are harassed online should stay off the web. Last July, he was permanently barred from Twitter for violating the platform’s rules against hate speech and harassment.

So when Threshold Editions, a conservative imprint at Simon & Schuster, gave him a six-figure publishing contract, the blowback was swift and furious. There were calls for a boycott of all of the company’s books, a vast catalog of some 2,000 titles from 50 imprints. Some of Simon & Schuster’s authors — including Karen Hunter, Danielle Henderson and Bradley Trevor Greive — denounced the publisher on social media. The Chicago Review of Books said it would not review any of the company’s books this year.

The criticism highlights the minefield that publishers face as they try to court an emerging market of young conservatives who identify with extreme right-wing stances on issues like immigration and gender equality — positions embodied with devious, irreverent glee by Mr. Yiannopoulos — that they feel are undermining the nation. Many liberals and moderates say, however, those positions amount to outright racism and misogyny.

And the issue has cast an uncomfortable spotlight on a lucrative but often overlooked niche within the largely left-leaning publishing world. Every major publishing house has a conservative imprint — Penguin Random House has two, Sentinel and Crown Forum — and maintains a stable of right-wing authors who may not attend literary festivals or mingle at the National Book Awards but command a sizable audience in red state America.