That is absolutely ridiculous.
Everyone gets mad, and takes out a bit of their frustration in the chat, if its a sentence or two then I do not see the big deal. If its constant harassment, name calling, AFK, racism, spamming, trolling, feeding, etc, they should get banned. But I am sick of all these pity reports and bans that are happening because people want to ruin the game for someone else.
Everyone gets mad, its a video game, not every single player is going be kind and sweet talk everyone, especially if people don't communicate, participate in team fights, etc.
They need to fix the tribunal because granted, yes its a free game to play, but alot of us spend a large amount of money on Riot Points on skins, champs, etc. and we get screwed over by people who just want to ruin everything for everyone else.
TL;DR Please only ban people for constant harass, spamming, trolling, feeding, AFK. If you curse at a teammate a few times, they most likely deserve it and should help with the team instead of playing for themselves. Afterall, this is a team based game, and with no team, you will not win!