Let's first consider the premise: I don't know if Rossi deliberately slowed Stoner.
If we assume that premise, however, there is a huge difference between the two situations.
If Rossi slowed Stoner, he did not do so to favour a third rider and to hurt the championship hopes of someone he doesn't like. He did it to better his own position. The latter is the aim of racing. The former is not.
Well, can we apply your premise of LS08 towards Sebang15?: "I don't know if Marc/Rossi deliberately slowed..."
If we start from there then we must accept both LS08 (as you do) AND Sebang15 as acceptable norms of "racing".
The problem I see is that you've applied a double premise of the double standard variety. For LS08 you start off with the notion of honesty, for Sebang15 you start off with the notion of guilt.
I've argued that Rossi deliberately impeded Marc (that's the other way around what you argue). Let's juxtapose the motivations for a moment here. Rossi needed that 3rd position but didn’t have the pace to outright secure it. (I don’t believe he had the pace to challenge for the win nor 2nd). That means Rossi recognized he needed to deploy the strategy exactly as he saw Stoner, his only chance to secure 3rd (16 points) was to impede, obstruct, and disrupt Marc. The problem arose when pesky Marc wasn't eliminated like unwitting Stoner, which required a more desperate tactic culminating with the eventual attack to crash Marc out.
I'm sure you just read my formulation like I'm some crazy person, based on your assumptions that Rossi is incapable of such a Machiavellian scheme. But I would point out there is a historical account of Rossi employing such a strategy (LS08). Second, this argument above has as much validity as assuming yours, which paints Rossi as honest Abe, just trying to "race for position" honorably when in fact there have been documented cases where Rossi has admitted to ruthless cunning strategies, I'm reminded of his endorsement toward tire development that he viewed to be detrimental to his rivals which he later admitted was a tactic of competitive strategy. It's as likely that Rossi strategized to impede Marc at Sebang given he had dedicated quite a bit of thought to the prospect he faced from practices, not dissimilar to the prospect he faced and formulated during LS08.
Regarding the vid you posted of Marc's press conference. That's a very interesting clip, I've watched it several times, and again right now. You are focused on him conceding the mistake based on (as he put it) the sketchy conditions, a "wet patch". I'm not sure how you go from there to accepting it was penalty worthy. Marc makes the case the conditions were such that even with the best skill on display, rather than infallibility, the conditions played a part, as he points out even other were effected by these "difficult conditions", that at worst produced un-penalized racing incident, the message being, not penalty worthy but rather reasonable racing incidents. You seem to be mounting the case that because he concedes the conditions induced a mistake that therefore it was worthy of punishment. Truth is RCV6, that these "mistakes" are rarely if ever punishment. The best example of this is Jerez 11. The supposed message from Race Direction is, we accept that such tricky conditions produce unfortunate unintentional situations. Therefore the penalty illustrates RD deviated from that norm, I argue because it involved Rossi. I'm aware you position is that it was done based on a plurality of penalties. Which is exactly why I make such a big deal about those incidents tgat have gone unpunished. We could reasonably point to a plurality of punishments Rossi would have received had Race Direction been consistent.
Anyway RCV6, I think we are both compelled to present our sides of the argument, which as I said is appreciated.
If you live in a glass house don't throw rocks.