That theory was mentioned often in the early 2000s when most people stilled used pseudonyms online but it has been debunked since then by the many people who feel perfectly fine spouting the same kind of hate on social media under their real name and sometimes even in video form.

Physical repercussions do not exist in the real world for anything but the most extreme of actions. If anything the culture of lying to each other's face (a.k.a. being polite) and looking away when abuse happens makes abuse very common in the real world, just ask your average minority or retail worker.