I generally simpathize with players having a big ambition, but in this case I interpret this as selfish and egocentrical.
Cristiano Ronaldo has (or had) the respect from Man Utd fans due to this talent and achievements in the past. He is undoubtedly still a great player.
But he is 37 yo, closer to retirement and like it or not, there are better and younger players that will outclass him sooner or later. Is is worth playing CL and scoring a few goals by sacrificing his reputation with the last fanbase that still respected him? I honestly don't think so.To the contrary, he could have been seen as a true hero by taking leadership of a crappy locker room and giding United to a brighter future, like Zlatan did with Milan.
I believe this is enough evidence to prove that he indeed wants to overpass Messi's legend somehow.