MUNICH — David calls himself "a warrior for social justice." But he tries to stay an anonymous warrior. Having your tires slashed, your wall spray-painted and your life threatened will make a person cautious.

Clearly, there are some people who suspect the self-styled "do-gooder" for being the whistleblower that he is. In the interest of trying "to make Facebook a more humane place," David and four of his friends "collect" racist and contemptuous comments made on the social networking site and then report them to police and employers. His detractors say that "he fights for the abolition of freedom of speech." He clearly views it another way.

His laptop contains hundreds of screenshots of rabidly racist comments as well as the profiles of the people who made them. Nearly all of them have used their real names and uploaded photos that can be viewed by anyone — photos of their families, friends, their activities and vacations. Many also supply information about their employers.

They seem not to care if they are recognized online. One of the comments made underneath a photo of the truck in which refugees suffocated in Austria reads, "What a terrible pity that only 70 of these freeloaders died a miserable death." Another Facebook user advocates the building of concentration camps and adds, "then gas these bastards."

There are thousands of comments like these on Facebook. David says he just can't abide them. He has documented the most extreme comments since visiting a refugee camp, and has reported these to the police and sometimes even informed the employers of the commenters. A few investigations for incitement are already in progress, and there have also been instant dismissals for some employees.

Because David has red-flagged guilty parties to their employers, he's become a target. They accuse him of wielding a digital pillory against people, and criticize him for being too cowardly to show his face. David has difficulty understanding these accusations, saying he very carefully checks to make sure that the comments aren't merely one-off juvenile aberrations but that they are consistent and representative of the person's online commentary.

Those who have "liked" extreme right-wing organizations and have openly posted comments against refugees for months have to answer for their attitudes, David says.

But he doesn't think it's fair to call him a coward. "I would love to stand for my convictions with my name," he says. "After all, I am not ashamed of what I do. But when you receive emails that outline how exactly you will be killed on a daily basis, you think twice about revealing your identity. It's easy to confuse bravery with stupidity."