Excuse me while I roll up my sleeves...
Well, it never made sense to me that the Enterprise crew jetisoned Spock's body at the Genesis planetoid in the first place. Why wouldn't they keep the body in the Enterprise morgue, and deliver it Spock's family/Sarek, or at the very LEAST deliver it to the Vulcan Starfleet representative, for a proper Vulcan burial/ceremony?
It was pointed out earlier in this thread that it was irradiated. One could make the case that it's Starfleet protocol to dispose of the body due to quarantine issues.
And they gutted a torpedo tube to place the body inside it.... why? On a starship with hundreds of crew members, a medical bay and the ability to perform surgical procedures, you know they had coffins on board. Or at the very least, the ship's replicators could create one as needed. The torpedo seems to be a plot device, just so they could shoot his body into the void. Unless this was standard Starfleet procedure (to jettison dead crewmates when on a mission, when away from a Starfleet member world or space station for an extended period of time).
Again, radiation leakage...you wouldn't put Spock's body in a coffin to take home.
But your second explanation works as well.
...And then there was NO representation of Spock's Vulcan identity at the funeral. Kirk spoke briefly about how HUMAN Spock ultimately was. Amazing Grace was played, on the bagpipes. Which is a Christian, Western Society tradition (I know, bagpipes come from Scotland/Europe). Amazing Grace is a 100% relatively modern Christian song that speaks about overcoming life's troubles with divine help, and ultimately the promise of eternal life in Heaven with God. It would be highly inappropriate to use this song at his funeral, UNLESS:
1) Spock had converted to Christianity, or...
2) They lyrics had been changed over the years, to remove the religious connotation, or...
3) Spock just liked the song and would have wanted it to be played at his funeral (we later learn in ST 6 that Spock had a painting of the Expulsion from Paradise in his private quarters... he referenced it as an Earth myth that reminded him that all things end).
Agreed, that's Nicholas Meyer tugging at audience heartstrings. The story goes that composer James Horner begged Meyer not to include that, because it didn't fit the sci-fi situation, to no avail.
My explanation? It was Scotty's idea and desire to play that, due to his own heritage.
As for Kirk calling Spock human, we know that is a compliment that Spock never truly understood. Kirk had to explain to him in ST6 that "everyone's human" in the way that he uses the term (and therefore Klingons are not animals). While Spock originally aspired to be as Vulcan as possible, Kirk's compliment suggests that Spock was really like us all.
...And even though the torpedo tube did not somehow disintegrate on atmospheric entry on the Genesis planetoid... it didn't have thrusters to help it decelerate or even "land", and it would have CRASHED into the ocean or land, and certainly been shredded to smithereens at impact.
...And even though it DID survive its crash landing, the corpse inside most certainly would NOT HAVE remained intact. It would have been green fleshy goo and pulverized bones inside the torpedo tube.
David's line covers this: "Gravitational fields were in flux...it must have soft-landed". Imagine high gravity to snatch the tube from space, and ligt gravity at the time it hit the ground.
..And since a Vulcan's Katra was a known "thing" in the Vulcan society, then the only way Sarek would have known to seek Kirk and read him the riot act would be because it WAS commonly (or at least, not infrequently) acted upon to somehow preserve the deceased Vulcan's mind/spirit/essence. But there's no indication that Spock's Katra communicated with Sarek for Sarek to be aware of what was really going on... because Sarek didn't know any of the details. Kirk didn't know what Sarek was talking about, which meant that probably NO HUMAN would know about the Katra... which means that Sarek should not have been upset with Kirk for not knowing about some private, ancient Vulcan ritual that was never discussed with outsiders.
Yes and no. You are correct that no human knows about the Katra, but Sarek originally thought that Kirk was actually carrying Spock's Katra, and therefore would absolutely know what he should do....hence the riot act. "You were the last one to be with him"..."Because he ASKED YOU to...because he entrusted you with his very essence....his Katra"
Also, Sarek knew Spock's body was found on Genesis because the
Grissom informed Starfleet as soon as they discovered it. Captain Esteban is a by-the-book kind of guy, so he was in touch every step of the way right until it was jammed prior to its destruction. So back home, everyone knew the body had been found. They just didn't know it had regenerated into a child.
...and exactly HOW was this used in day to day Vulcan society? Grandma is on her death bed, so she does a quick mind meld with a family member to pass on her spirit... and then what? Did the recipient now have their relative's mind living inside of them?
It's never elaborated in canon, but authors at the time (Diane Duane, I think?) tackled this in non-canon novels, so take it for what it's worth. The notion was that yes, the katra would go to the person they were closest to (usually a mate or family member), and then that person would somehow lay the Katra to rest in some ceremony, kind of adding all that essence with the essence of the people...Minbari style.
We have some evidence of that with Sarek's line: "Forgive me, it is not here...then everything he was, everything he knew...is lost." That suggests that Spock's knowledge could have otherwise been preserved, even in death. This is before anyone knew that Spock's body was regenerated. So I buy the novels' explanation.
The closest I THINK we got was when Sarek mind melded with Picard, and then Picard allowed Spock to mind meld with him and experience Sarek's sssence/mind/Katra ??? So, did Picard possess the mind of Sarek, and then hand it over to Spock?
No, you can't make copies of the Katra. Picard gave it back to Sarek...but some memories of the experience remained with Picard, and that's what he shared with Spock.
Whew!