In Riots eyes
If Riot's logic is to ignore and report verbally toxic players, what is the point of banning them. Ultimately if you ignore them by muting them then they cannot effect you for the rest of the game. If you are going to tell me because they lower the standard of communication, then by that logic players who do not say anything should be banned as well. This is of course assuming the player really did mute the toxic person, instead of antagonizing. Why not let everyone have their fun? Why value a strict policy that leaves many unhappy, instead of having one that relies on the player to take true responsibility?
Even reporting trolls is feeding them, if we all decided to give trolls literally 0 play, by simply muting them and ignoring them. I think that would be the best way to defeat toxicity.