Your claim that "antifa" exists solely to fight white supremacists is absolutely incorrect. Hooded leftists have been rioting at G-7 and G-20 meetings for decades.  The most recent example was the G-20 meeting in Hamburg in July where they set street fires and looted stores (Source: CNN; see link below).

 http://www.cnn.com/2017/07/07/europe/g20-hamburg-protests/index.html