I, the 3rd speaker for the negative side, believe that... whatever topic is, like:
I, the 3rd speaker for the negative side, believe that warning signs and railways should be removed because this will help the process of natural selection.
Rebuttle:
The affirmative side stated that, "______", this is incorrect for "___" and "___" etc.
Eg:
The affirmative side stated that hand rails and signs provide safety for everybody, why should we risk lives just because some people are not as smart as us? We should risk these lives because if they are not smart enough to not fall off the edge of a bridge then we do not want them to pass on their genes to their children. Think about those poor children, would you want your child being that stupid? No. So yes we may be putting lives at risk, but we are helping the future generations to be more aware and increase our rate of advancement as the human race.