Quick three questions for the ones who voted no:
1. Do you think the anti teamkill system was made so you can help civilians escape or harm your team mates?
2a. If your answer was 'no', what would you do to prevent the anti teamkill system from being exploited like that?
2b. If your answer was 'yes', don't you think helping someone to attack your team is, indirectly, the exact opposite thing the anti teamkill is supposed to prevent?
Of course civilians can pick any side at any time, I don't know why you guys are saying that like it had been questioned. They can pick any side because any side can confront them. And this is not possible while a member of one of those sides carries the civilian in their vehicle.