Progress happens one funeral at a time, and new generations need the space to grow and find themselves without the tutelage or control of the elderly. Even a lifespan of 200 years would be catastrophic socially - and probably physically, too.

It's been bad enough over the past forty years with leadership failure to move over and allow ideas that are better adapted to the reality of a changing planet. Humans typically gain political and financial power as they age, and this would result in a gerontocracy, as if we don't effectively have one already.