Yes it is unfair, this is life. Yes riot expect you to act like a robot and suck it up. Either learn how to mute, or say a response that is non offensive. "Why are you saying that? Don't you think that's a little overboard? Just because I am doing bad doesn't give you the right to label me autistic."
Yes if you are in the minority the game will be cruel to you. Many people play with their friends. If you play flex you will get banned more often for being curt or sharp with others than if you play solo. This is because the amount of bitch you can get away with is close to none. You would be lucky to get away with saying something simple as, "Please ward river before pushing lane." nevermind something with a bit of an edge to it.
Yes 'toxic' players are in the minority of the game. When I say 'toxic' i mean if you aren't in a group of friends and are trying to make friends here on league of legends. Most people here have a 'mightier' or 'holier' than thou complex and do not care about your suffering. If you want to make friends here you have to meet them outside of a game first.
Sometimes you are better off not dealing with whatever is causing to be pissed off than grow to accept it. You may need to grow to learn ignoring what other people say/tell you to do as a part of growing up. If you deem yourself unfit to judge yourself. then yes you are at the mercy of your 'peers'. If you are intelligent and consider your choices, [even the dumb ones] before and after you make them, you just need to grow up and decide that some battles aren't worth fighting. You can judge your own gameplay. and if not, perhaps look to see if they have a reason for saying what they did.
It's not worth fighting a company or children over a video game. This includes conversing about it. While I understand your response as a human being, unfortunately the game sees you as in the wrong. I also understand in a game that is time based, it's hard to articulate thoughts and complex sentences that don't hurt someone else's feelings. A lot of these people would actually be better off understanding that if what you said is true they are better off listening to it rather than getting annoyed. Chances are saying something like "You're retarded" is not of any use to anyone even you however. If you often get caught insulting people instead of doing/saying things that are beneficial to the game then chances are you deserve the ban.
"Could we please group up and not get picked off again?" "I really don't want to start dragon if river isn't warded." "I don't think it's wise to start a fight with the enemy with no ult." "Why are we pushing while they have baron?" "I don't get why the tank and support ran away with full hp while everyone else is fighting." These are the sort of things I feel are fair to say, and chances are if you let "You're retarded" slip out without much harassment at all then you are actually highly toxic. Even I cuss every now and then but I don't get 14 day sentences or even suspensions. I am not saying this as one of those "holier/mightier' than thou people. I am saying it as a person who has had an account banned in my first season of play.
As you grow up, you'll learn to articulate the reasons behind your frustrations and not just your frustrations. Nowadays when someone says something like "You must be autistic" I reply "Muted/Reported" "Just because I don't agree with your plan doesn't mean X" or "I did bad this game, but you seriously need to lay off, I am not a pro." Part of someone's frustration with you and yours with them should lie in a function of the game. If it isn't then you are already talking to someone without any form of sanity and you need to preserve yours by muting/ignoring without any recourse. As a bigger man you can suck up one comment long enough to mute hopefully. If not well... then maybe you need to start working on your temper control.