Eh, I may have exaggerated on part about mistakes. Fair enough, I don't want to hunt down posts to try and prove it, anyway.
I'd argue that's the Overwatch team grossly overestimating how attached people get to certain play styles than people intentionally going against the point of the game.
I've actually refused to swap to a different hero in comp myself. It's not always being selfish; in fact outside of one tricking (Which is again not even against the rules, Blizzard's inconsistent rules aside) it's often because the people who ask are not asking nicely. They're angry and looking for someone to blame. It's far easier to assign blame to everyone else than it is to check one's ego at the door and do some introspection mid-game. Hell, I've been guilty of it myself before. On the other hand, most of my experience comes from people asking me to swap to a different support hero, from Mercy or Moira/Brigitte to Ana/Lucio or Zen. I cannot play those heroes, and you do not want me being a wet noodle floundering around and doing literally nothing because I can't hit anything. I tried, I can't do it. I imagine others feel the same, and are probably tired of having to hear/see people ask.
I'm not sure this applies, but I always believe that Overwatch competitive should never have released. But since it did, the dev team did both the players and themselves a disservice by not making six-stacks a requirement. I can think of several hot button topics over the years that would have been solved if people played in regular teams. But being a team player doesn't mean bowing to your team because they said so, no one on your team knows your capabilities better than you do. If someone asked me to play something I can't, I'm probably not going to do so because I know what I'm capable of. They don't.