Hey there! Before I knew all the details, I was actually on your side.
Even so, I also have been punished for my behavior, and even though I'm reformed, I can sympathize with your aggravation.
To help ease your frustration at what you think are "bullshit reasons" for getting banned... I want to point out parts of The Summoner's Code that your behavior violated. This is the same Summoner's Code you agreed to before you even play any games on your account.
#3
##Facilitate Civil Discussion
###...be mindful of how you present your point of view. If a player feels strongly on a subject, don't get caught up trying to have the last word. Just state your side and exit the conversation gracefully rather than give them the opportunity to pick a fight.
######I especially struggle with this one on the boards. It's something that I have to work harder on.
(In your case, instead of just saying "hey, bullying isn't cool guys! top, you should mute them. don't pay attention to bullies." and then moving on, you spammed chat about it and continued to go on about it for the duration of the game. You also insulted other players after the game, which violates this section of the Code)
#4
##Enjoy Yourself, but not at Anyone Else's Expense
###...If two players on a team start fighting, good communication and teamwork become nearly impossible. Once communication breaks down, the likelihood of victory is drastically diminished.
(In your case, you were in constant disagreement with the enemy team and you wouldn't let it go. Yes the mute feature exists, but your team shouldn't have to mute you for an argument with the enemy team that fills up the chat, which is how you violated this section of the Code)
#6
##Show Humility in Victory, and Grace in Defeat
###Having a great game is one of the biggest joys that League of Legends can bring you. But always bear in mind that when you're relishing that landslide victory there is someone on the receiving end that is probably ripping their hair out. While it's alright to celebrate, make sure that you keep any gloating (or any other mode of self-indulgence) out of all chat. Instead, thank your opponents for the game. After all, despite their best efforts, they just made you a very happy person.
(In your case, even though you were "defending" your opposing laner, a lot of your chat was more of 'tooting your own horn' than really defending him. "I'm just so good and so strong there's nothing he can do." was the attitude and that kind of gloating violates this section of the Code)
#7
##Be Resolute, not Indignant
###...If you end up in a game with an abusive player, don't lower yourself to their level. Instead, politely ask them to calm down. And remember, even if you're having a bad game, quitting or going AFK just ruins the game for the rest of the players. If someone's really starting to bother you, the mute and ignore commands are always there to resolve the situation.
######this one might be a bit redundant, but it's worth pointing out that it applies to this part of the code too
(In your case, instead of just asking the enemy bullies to calm down or stop and then letting it go, you kept at it which can - and probably did - exacerbate the issue. By forcing the conversation to extend the length of the game and for insulting other players about it in post-game chat, it goes against this section of the Code)
Well, I hope this cleared up some of the confusion about why you were punished in this instance.
I do genuinely sympathize with you because I know that your intentions weren't entirely malicious. Even so, we are all bound to abide by The Summoner's Code and have all agreed to do so before we started playing. I hope you do continue to play on a new account, and going forward you'll have the tools necessary to avoid a situation like this in the future.
