Then why did he testify under oath that he would cut Terri's arms and legs off and put her on a respirator if necessary to keep her going?
So9
Congratulations for swallowing the propaganda, which you demonstrate quite obviously by stating the amputation claim with no context whatsoever. Nevertheless there are several answers to the question.
First of all, he presumes that with proper therapy Terri can be at least partially rehabilitated. That's the primary difference between Terri and his mother. It is one thing if a respirator is intended to be a temporary measure; another if it is permanently necessary.
Secondly, we cannot speak to the wishes his mother may have made. And since Terri did not have a living will and a durable power of attorney, we cannot say in her case either. Who knows, maybe the mother did those things.