Yes, that was the point. Even if there's something you can do about it after the game, you'd still rage when you saw it, making the game generally miserable.
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...and no raging does not effect games like trolls. Competitive people get worked up, that's what ranked is for. Competitive people! If someone is raging then just mute them. You can't do anything if someone is trolling. Sounds to me like you should stay in normals.
This. This is the problem. You don't understand the effect you have on your teammates by raging, and you try to hide behind the mute button, as if that gives you free reign to be a dick. It doesn't.
No, you can't do anything about trolls. But you can stay positive instead of giving up. You can ignore the troll and do the best you can with the rest of the team. Or you can let your attitude drag down everyone on your team. The responsibility for that choice is on you and your self-control or lack thereof, not on the person who made you angry.
You're competitive? You want to win? Don't rage. Better to have one troll member and a solid, coordinated 4v5 than to just trash the whole game by being toxic.
Or else, maybe you should just stay in normals. ;)