A toxic player should plead guilty for less punishment.
It has come to my mind lately that some people do regret being toxic. As human beings, we all experience outbursts of aggression and give in to our emotions that drive our actions to being non-player friendly. I feel that if a summoner knows that he/she will be reported for this, they should be able to report themselves so that if Riot does happen to punish said toxic player, they will receive a lesser punishment for acknowledging their actions did not follow the summoners code.
Edit 1: I understand this can be abused. However, if it was possible, riot should be able to see on average how toxic or not this player is. So if they report themselves while they usually never show toxicity, they should be given a warning or something along the lines. If it is overused though, they should be given harsher punishment or they cannot use their "get out of jail free card".
Edit 2: Racism and any forms of hate speech should have zero tolerance.
Edit 3: Verbal statements telling people to end their own lives should also have zero tolerance.