I think the only ones that are "sad" are those who saw Go very philosophically, like if it was more then just a game with set rules that can be computed.
Science fiction lied to us. It is science fantasy. A fantasy where you have human away parties and depictions of human agency roughly analagous (albeit glamourized) to the role we have always had bringing history up to this point.
Some people value human agency (1) and the human condition and want to preserve it almost for ecological reasons - it is the world we know, and the only one with meaning. Others I think fear death or hate injustice and (optimistically) see technology as a way to solve all these problems once and for all. Human (2) pride be damned (3).
1) possibly mainly white men, since we apparently have more of it
2) (White male)
3) Sweeping blanket statement I know. Sorry for the identity politics bit too, but you cannot really say anything on the human condition without someone saying or thinking that is is a different affair for other people.