[Nursie]

I think most people who don't want to be extend life are actually motivated by extreme fear of death.

A fear so profound that they've reasoned themselves into a corner, that this way we live must be correct and cannot be questioned, because if we start to question whether death is necessary after a 'natural' lifespan, whether research into prolonging life might be possible and might not actually not be a ridiculous endeavour for a few madmen, then that deep dread they cannot speak of may return and consume them.

Beyond that your comment is full of odd assertions - yes, people grow and change, but no, that doesn't imply discontinuity or repeated death.

Your older relatives are living in ageing or aged bodies, including their brains. Their experience of life is not necessarily what we could expect if we were to be able to put off the effects of age indefinitely.

Edit - but I'll take your few centuries over what we have now, as a starting point :)