The person you've responded to never said we should live forever, nor did they say they hate the fact that people die; rather, they said they hated cancer. That's an important nuance you left out from assertion, isn't it?

Sure, you may not want people to live forever, but that has absolutely nothing to do with the above comment; indeed, what you've said might be viewed as somewhat callous when considering the context that someone has revealed that they have terminal cancer.