Exactly. Rossi raced Stoner the same way at Laguna Seca 2008, Lorenzo the same way at Motegi 2010 when VR was out of the title race (I thought he was entitled to do so, and said this at the time), Colin Edwards rode as a blocker for Rossi when they were team-mates (as I saw when I re-visited footage of the race during which Pedrosa took Hayden out in 2006 for instance), Rossi got his lead over Lorenzo in 2015 with everyone in the field trying to beat Lorenzo in the first place, and for that matter no-one gave Mick Doohan anything (and nor of course did he ask for anything) when he returned for the last 2 races of 1992 and only he could beat Wayne Rainey; he had absolutely dominated the title race before his injury at Assen in that year.
If there is an unwritten rule it is that you shouldn't put a championship contender at risk of crashing out by an unfeasible move, which MM didn't do at PI 2015 and probably didn't do at Sepang, after which he was pretty much admonished in regard to racing a contender for position, apparently after successful mind-reading by RD. Rossi himself of course took out Stoner who was leading the championship at the time with an egregiously stupid and unnecessary move at Jerez 2011 which could seriously have affected Stoner's title chances but Stoner somehow ended up being the bad guy in that incident as well.
Either it is allowable to race legally for position or it isn't, I don't see how the ambitions of Rossi and his fans for him to win an extra title or whether MM has the "correct" attitude to Rossi and his ambitions come into it. Each race is supposed to be an entity unto itself anyway.