Twitter stirs debate as 'troll' banned over racist abuse

"Danielle Citron, a University of Maryland law professor and author of a book "Hate Crimes in Cyberspace," called the incident "a learning moment."

"I applaud Twitter for its approach in this area," Citron said. "If you chase people offline with racist and intimidating speech, that's too much. Twitter and other platforms are contributing to social norms on free expression.""