League of Legends penalty system?

Permanently banning someone for getting frustrated at a teammate that clearly gave up on the game is absolutely ridiculous. I didn't even say anything extremely offensive like telling him to drink bleach/kys. All I did was call him a degenerate and tell him that he's a coward hiding behind his computer trying to agitate others(also told him I'd rattle his teeth around if he attempted this in person). It takes far too much energy to deal with this kind of crap for the amount of times it happens. Everyone is bound to break and just let loose on one of these assholes from time to time. Also, If he didn't want to read what I was saying, he could simply mute me. To sum up this message, I didn't say anything extremely offensive, and the mute option is there for a reason. Let me know what you guys think about a permanent ban just for losing your temper.