Is Sarang a complete idiot?

[Kein]

Or did he just not take Computer Science classes as a kid? Or anything remotely based on real science for that matter? If he did, he'd know that cut-and-paste and copy-and-paste both copy the original.

He and his followers should've changed their motto to "We put our faith in the reality of cut-n-pastey!", seeing as they tried doing that IRL.

I guess you've skipped all the notes in the game and just went through it? Sarang explicitly mentioned that a copy will be identical or very close to the original right after the process and/or short after. But with time the difference in experience will alter the development of their conspicuousness, of their self, thus there won't be any more two similar copies.