Would it ever be acceptable to kill zombies?

Before you do the knee-jerk "yes", how long would it be before the average person would be willing to allow vigilantes to go out and start culling walkers from the streets? I mean right now, we have violent, non-communicative individuals who are locked up in mental institutions and it would be very wrong to start hunting them. Society might view zombification as a mental onset illness that affects people and doesn't strip walkers of their human rights.

My personal opinion is that the #1 reason for the success of the zombie outbreak would be that society would deem it wrong to take out walkers until there wasn't a society left.