Why Arnt There "Key Words"

I personally think there should be a set list of keywords that if found in a players logs whether it be joking or not should be a bannable offense. I for one live with a autistic individual who is non verbal, Thus I take the word "retard" VERY seriously and am getting tired of people using the word like it means nothing or like its okay to label people as such. Im sure we all have had our incidents in which a player just used that one word that lit a fire in your belly. So im now here asking YOU Riot, what can be done about this. I understand i can always mute people if they start being offensive but that still lets them get away with it and continue to think that its okay to use derogatory terms and not have to suffer any consequences. I also understand you cant just ban people left and right all willy nilly but it is NOT okay for people to get away with this kind of thing.