Since playing arma 2 I've found that there are certain people who enjoy to shoot friendly players. This tends to happen for a number of reasons, if you kill one of their ai team by mistake, if they want to get into a helicopter before you, or just out of boredom or frustration. Other times while playing a CTI they will start to destroy the base so no one else in the game can continue fighting.
I really dont understand why there is no real solution to quickly deal with this. Games like counter strike have a very good system to deal with this, after a certain amount of friendly fire the offending player is banned from the server for 24 hours. This means that most players try hard not to kill team mates even by mistake. Counterstrike also gives the player who was killed the ability to penalize the player who killed them by freezing them for 10 seconds or putting a marker on them so others know which player it was. I know that people who run servers want them to be accessible to everyone but these types of people seem to run out of control with no way to deal with them unless there is an admin in the server 24/7. I'm sure that a friendly fire limit could be set up so this doesnt happen..