Why are antis so stridant and unreasonable?

They have literally no argument. Logically communism just works. When you lay the facts out, however, antis will get riled up and threaten you while babbling about historical strawmen. To hear an anti tell it, communism leads to immediate mass death, like it's a plague rather than the most logical way to organize a society. Does anybody know why they get like this? Is it just the result of a low-IQ or is something more sinister going on?

If the Holocaust isn't real, then why did 2/3rds of European Jews ``disappear" during the war years?