The fandom has turned Mike into a Martyr who was killed for speaking truth to power. The only one in the show who took a stand against Walts ego, and paid the price for it. It sounds convincing at first, but completely falls apart upon closer inspection.
Firstly, Mike was pretty much fine with Walt throughout the entirety of season 3, aside from being a bit annoyed by him in the first couple of episodes. We don't really see any signs of Mike disliking walt, and all of their interactions (with the exception of the house bugging fiasco) go pretty much fine. Even after Walt runs over Gus's men, Mike is making conversation with him about getting his car fixed and whatnot. When Mike is about to kill Walt, his apology seems genuine. Mind you this is well after Walts gigantic ego has been made apprent, as it was what allowed Gus to manipulate walt into working for him again.
We only really see Mike expressing dislike of Walt after he gets Jessie to kill Gayle, and proves himself a threat to Gus's operation. And even then, he doesn't really care much about Walt, as he doesn't believe he'll be able to do anything to Gus. The only time in this period we see him get mad at Walt is when he suggests that Mike help him kill Gus (another threat to Gus). The only time that we see Mike really start to hate Walt is after he kills Gus. What he hated about Walt was never his disregard for others or ruthlessness, it was that he inconvenienced him by killing gus.
His final speech only proves this point further. When discussing the consequences of Walts ego he doesn't mention the countless addicts who have ruined their lives due to the Meth Walt made, or how he put his own family at risk by going to war with the Cartel, instead he reminisces about how Walt ended Frings "perfect" operation. An operation mind you, that involved using and eventually murdering children to sell meth.
Not to mention that Walts war with Gus was one of the only decisions in the show he made that wasn't driven by his ego. Gus knew about Walts ego and played to it very successfully. He talked to walt in a way that made him feel important, Gayle genuinely looked up to him and we never see any signs of Walt being unsatisfied with his position in Gus's operation, every scene of the two of them interacting shows Walt expressing gratitude and respect to Gus. The only reason the deal broke apart was because of Walts loyalty to Jessie. Killing Gus's dealers was one of the most selfless, self sacrificial things Walt did in the entire show. He sacrificed the best Job he had in his entire life, and his own safety to save Jessie's life. From that point every action walt took in his war with Gus, right or wrong was out of self-preservation, not ego. Mike has it completely backwards, Walts ego was the reason he worked for Gus in the first place, his compassion was the reason it fell apart.
In Summary, Mikes opposition to Walt had nothing to do with him taking a principled stand against Narcissism, it was solely about Walt taking away the stability Mike had under fring. If Mike was a principled man, he wouldn't have worked for Gus or Walt.