I value team comp and the enjoyment of my team, which is why my most played hero for my first 55 hours (never played beta, so this is from scratch) was Mercy. I only recently surpassed her with Zenyatta, but she and Lucio are still way up there despite me not particularly feeling like I need practice with them at this point. In fact I think it's silly that I have to preface what I'm about to say with this stuff, but that's how it is, people are insanely emotional about this topic, so I have to start with "I play Mercy a lot, but...".

Anyway to an extent, Placeholder's comment rings true: this is only quick play, and it's the only place where a person can practice or try out wonky things before ranked comes out. If I want to get better at a certain hero and even enjoy myself, I have to impose my will sometimes. If this means (for example) I picked Genji first and some other guy decides to pick Genji as well, then I sometimes say fuck it and go with it. It sometimes works, and sometimes it's close. If it starts getting bad, I'm always the one who ends up switching, and not even because I feel like I'm the worse Genji. I won't aggressively tell the other Genji to change, because I refuse to be the sour cunt that upset or even drove away from the game a random stranger for playing a game differently to how I think they should play. That's not what a community is about.

Even when ranked comes out and one selfish player's decisions might cost you some rank points, you can still be constructive. And what about people who just suck at the game? What about people with disabilities who can only play one hero? Don't be judgemental and self-righteous. Let people know (not in a cunty fashion) that they could be helpful in a different way, or if you have no patience because you must win at all costs and must improve your rank and GAMES AREN'T ABOUT FUN, MOM, then just disfavour the player so you don't match with them again. If you dislike toxicity in team games then don't become part of the problem.