>Human beings have natural
>violent and
>selfish inclinations which we
>attempt to
>overcome through reason and
>civilization.

I will resist the temptation to paraphrase the entirety of Daniel Quinn's Ishmael. Suffice to say, there is some debate about how natural our violent and destructive nature is, but there is little argument about how destructive our technology is.

>Hemlock is natural, but that
>doesn't mean
>you should make a milkshake
>with it?
>(milkshakes aren' t natural
>either).
>I don't see how you can reject
>cryonics on
>the principle that it's
>unnatural without
>becoming a complete Luddite
>and
>rejecting all medical science
>and modern
>technology.

Funny you should mention Hemlock. It brings up the point that human beings have been practicing medicine for as long as we have written history. Plants like Thyme, Elder Berry, Sage, Nettle, Fennel, and a great many others were used in ancient traditions and are still used today. So practicing medicine is natural. Immortality is not.
All life everywhere comes to an end.