Presidents have 4 year terms. Why can't people have 80 years where they're allowed to vote, and then lose that right forever? Or maybe they can be sent to a separate society where they're permitted to vote and debate things that apply to their own sphere, but must still follow universal laws set by a "central society", to prevent deeply immoral actions. For example, maybe alcohol is permitted to be permanently illegal in their society, but they still aren't allowed to lynch people or prosecute people without due process.
These are certainly very difficult problems to solve, and there are many counter-arguments to that particular. But I think there are solutions to these issues other than death, and I think many of those solutions are much preferable to death.
A society that adapts to become biologically immortal will find their own ways to adapt to dealing with zeitgeists and progress.