Gonna try and keep it short and sweet so:
I'm toxic, many others are, sorry about that, but I also want to play this game... contradiction I know but wait! I've got this idea that will reduce toxicity and keep people like me who have irrational keyboard seizures because of real life things like adolescence, exams, depression... (keep in mind these are just a few reasons why someone may be toxic, tilt is a common one).
Manual chat restriction!
I know when I'm in a bad mood in real life so I stay away from people, in League you are trapped with people which usually cause your toxicity in the first place. This is a bad scenario, and the immature people who due to this can't remove themselves lose control of their emotions from time to time and can say some inappropiate things. With a manual chat restriction option for the rest of the game that can't be reversed these immature people can remove themselves from the situation avoiding harm to both parties in the scenario.
TL;DR manual chat restriction because toxic people might not want to be toxic but are too immature to handle themselves.