Ian Keldon
Fleet Captain
In going back 25 years, Spock Prime would essentially be killing the James Kirk born at the start of the movie, and everyone else born into a life somehow altered after Nero's incursion. In exactly the same way that Janeway killed the Miral Paris born and raised in the Delta Quadrant in "Endgame".
That is an open issue in all time travel. The standard response is that the history as known is the "way things are supposed to go", and any alternation of known history is unacceptable and must be repared.
In short, Miral Paris was never "meant to be", and Kirk Prime was the way Kirk was "meant to be", and Spock Prime had/has a duty to maintain and restore (if necessary) history to the pre-incursion version as best possible.
How exactly does Spock have the right to do that? A Starfleet regulation which Janeway heard in "Future's End" from a 29th century time cop (who caused the very disaster he saught to avoid, btw) and then adopted herself?
The TPD is a Federation/Starfleet regulation. It is binding on all Federation citizens and Starfleet officers. Neither may attempt to alter the timeline as it exists pre-incursion, and must attempt to restore said timeline against any incursions that alter it.
When that Spock is a result of countless similar temporal incursions himself (one of which, in "Yesteryear", he did himself!)?
"Yesteryear" was an example of a "pre-destination paradox", in which the time-travel and subsequent effects were always "meant to happen". You will note that Spock Prime initially ceased to exist because he was not available to go back and save himself initially when the historians were viewing Vulcan history.
I guess you're right about Scotty - but I'm sure he thought it'd work.
Doesn't matter...such experimentation is a violation of ethical standards one would expect of a Federation citizen or Starfleet officer.