I'm not an expert on computers but doesn't the brain wallet provide a unique output when somebody inputs random typing like......
3903450EFZDFZOJF3405340F9ZDFF034T038TGERPJEPRFP034FZEFZEF03450324534508ZEFZOFJZ ELFJ345
In other words it would be unlikely anybody else would type that exact code in and get the same brain wallet results?
Humans are notoriously EXTREMELY bad at being random.
If you want random input, you should REALLY consider using some source other than your brain or body for generating it.