that's the bystander phenomena if I am not mistaking. The more people there are the less are the chances that someone will act; they think that their surrounding will act.
OFFTOPIC
the -2 rep is not for you as a person but for the post; it's no entertainment to see people fight (not in real life at least) and it's definitely not humorristic
The -2 are removed but for the next time please bring something that fits to Humor