“‘Why does the Ayatollah Khamenei of Iran have a f— Twitter account?” asks Mark Wallace, a rare lapse in language from a courtly man. “Why should the No. 1 state sponsor of terrorism be on f— social media?” [...] Mr. Wallace’s decade-old nonprofit, the Counter Extremism Project, acquired the Höss house and one next door from the Polish family that had owned them for the past 80 years. He declines to say how much he paid but says there were “at least 10 different family members across two houses, and many were estranged from each other.” The purchase “took years to accomplish because we didn’t believe it appropriate to pay a significant premium because of its Nazi history. As for his broader mission, he speaks of an “algorithm of evil” and wants to “make it untenable for social media to reward hate and antisemitism.””