I need to go so I have to write this in a hurry, but I will be back sometime later. (although, I am lately trying to stay away from these threads since they take up too much of my time

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Sorry, but how does individualism cease when society collapses? Are you saying that people return to baser instincts and therefore there is less potential to display one's individuality, or that evolution somehow removes individuality from humans? The former I could agree with; the latter I do not. Evolution wouldn't make people into clones with identical thoughts, likes and dislikes.
The second "choice" is possible, but I wouldn't vouch for it due to its largely unknown nature as of yet; the first is more along the lines of what I was thinking. What seperates the human from the animal is this sense of perpetual desire; the animals display some kind of desire as well, but they become happy when they get what they want, while humans in the large keep complaining and try to attain more things in an attempt to once again find the happiness. This is the everlasting process that can be said to have accounted for all progressions in human affairs: science, society, creativity, religion, morals, etc. And nothing happens to the individual at all immediately after the society collapses; like I said, the individual will still retain all of its properties. The problem comes up after many generations when the human has evolved enough that it can be considered a new species, because there is no guarantee that the new one will retain this characteristic that can be considered to "make" the human.
And I fully agree that society can perpetuate (as long as it changes to those within it) ad infinitum. Saying the "social machine is of more importance" though, suggests that we should act as society dictates - as though it is some frozen set of rules, which, of course, it is not. Society is made up of people, rather than being a 'thing' in and of itself.
Well, "being made up of people" and "being a thing in itself" are equal to exactly the same thing here, just as our bodies are made up cells and are yet something in themselves.
Oh, and let's test your hypothesis: I am going to try and convince everyone in my school to give me all their money so I can spend it on myself.
If you organize some rowdy orations Hitler-style, and tell them that you will use their money to do god's work, and keep repeating this procedure, I bet you will get some of their money.

I'm not saying it matters what they're changed to so much as the motivation behind changing them. Say a person wants to change themselves so they feel perpetually happy. Fine. Now, say society wants to change them so they feel perpetually happy. Not fine. There's no consent in that, and you have to question the motives of 'society' in this case. That's the impression I get from your "ultimate society" - that people's happiness is engineered to make them efficient and stifle discontent. Maybe I'm just paranoid...
Actually, you're quite right about that. This "ultimate society" should not feel happiness or sadness at anything, and should view everything with mathematical indifference. Regarding the consent of the people, I said before that forcing people into accepting may lead to rebellions and thus is not a good solution (but only because of that), but the few who accept it will essentially become the dominant beings in the course of history. The motivation behind changing things is that all the other systems lead to contradictions, as I said before.