But advertisers can also gain access to people associated with Facebook pages that perpetuate false, misleading or divisive information. For example, many people who liked two pages on Facebook that frequently defend the Confederacy are likely to be included in the Confederate States of America category that advertisers can target.

One of the pages, with roughly 250,000 likes, recently included a post declaring the Confederate Army “the greatest force that ever walked the Earth,” and another post prominently featuring a quote attributed to a Confederate general: “The Army of Northern Virginia was never defeated. It merely wore itself out whipping the enemy.”

Stephanie McCurry, a Civil War historian at Columbia University, examined both pages and found them littered with “fake history,” such as the suggestion that slavery was not the central reason for secession.

Despite their potential to offend, Facebook’s Confederacy pages do not appear to run afoul of the company’s standards on issues like hate speech. Some veterans of the digital advertising business said that as long as that is the case, it should be up to advertisers to determine whether to target categories composed partly of people who like these pages.

“At the end of the day, these gray areas are dictated by the advertiser,” said Chris Bolte, a longtime ad-technology official at companies like Yahoo and Walmart. Mr. Bolte said advertisers had every right to target the audiences most likely to be interested in their products and services, unless those audiences were “obvious hate groups.”

But Ms. Roberts at U.C.L.A. argued that simply by allowing Confederate States of America and similar pages to exist and then using this content to help advertisers target people with those interests, Facebook was blessing the views expressed there as legitimate.

“We can draw a line from content that proliferates on the platform to what is extracted and monetized, made into revenue flow from advertising,” she said. “It is up to Facebook to make the decision here whether to impede that process. Whatever they decide, it is no longer possible for that to fly under the radar.”