Security Dispersion:
In high security space, killing a civilian nets you -50 wp and a security status loss.
Once your security status is below -0.5 (after killing lots of civies) you are no longer immune to friendly fire in high-sec pub matches. Once your security falls below -0.8 you may no longer participate in high-security Pub matches until your standing improves (via PVE).

But, penalties are no fun, so positives are a better route imo:
The a portion of the isk pay-out is determined by the number of surviving civilians at the end of the match for both teams (as typically the attacking corporation wanted the facility and its staff).
But, there could be modes where the attackers want to eliminate all the civilians, each civilian giving bonus pay-out at the end of the match.
Perhaps there is a mode where the defenders are eliminating the civilians, but the attackers are trying to save them, netting differing payouts for both teams.