You are held to what you say/do
This isn't something you can simply ignore and overlook. I see so many rage posts on PB and let me lay it out for you guys.
Everything you say or do in game, regardless of what is happening around you, is 100% on you. What others say or do does not effect your punishment in any way which is only fair. You said that racial slur. You used that hate speech. You insulted and belittled your team. It does not, and almost never will, include what your teams do because they are held to the exact same standard as you. Whenever you are being punished, it is your actions that caused it and no one is allowed special terms from the rules Riot has put forth.
Be the bigger individual and move on. People will rage, people will feed. Sometimes this will happen. It ruins the game for others and no one likes it. Being equally toxic, being an equal problem does not solve anything. It never will. What do you think? That the person that is already int'ing gives a damn that you start int'ing? God no! Don't sink to their level and waste your time.
Nothing is wrong with this system because every single player is held to the same standards and given the same rules. If you don't want to get punished, if you don't want to be banned, listen to the warnings. Stop letting people get the better of you. At the end of the day, it does not matter what others do. it only matters what you do.