People’s willingness to modify their weight is irrelevant—the argument is only claiming that some people could improve their life expectancy by modifying their weight, not that they necessarily will.

The intention that led the insurance companies to create these tables is irrelevant to their actual usefulness to guide people’s changes in weight.

If anything, the data would be a more reliable indicator of how weight impacts lifespan if accidental deaths were excluded, so an assumption that accidental deaths were included is not necessary.

The argument merely claims that people within the standard weight range lived longer than people outside that range. This relationship could still be true even if the general population has overall shorter life expectancies, so this is not necessary.

If we were to negate this—if people’s weight-modification efforts were so harmful that their lifespans decreased—that could offset any increase in lifespan. That would deeply undermine the argument, making this assumption necessary.