I strongly disagree with the title of your post, and this part of it:
If someone intentionally feeds, they ARE going to do it again. Not tomorrow, maybe not the next day, maybe not a week after being suspended for it.
But they will, EVENTUALLY, do it again.
People change, people have bad days, etc. etc.
They already start with 14-day bans, meanining they only get one additional chance before getting permabanned completely. And I'm certain a lot of the benefit of doubt that players would normally get, regarding the feeder buster, is probably flying out the window after the first "conviction".
Plus, the "real" trolls, the kind of people that really just don't care about punishment? They're not even really affected by this, as you point out yourself. They use smurf accounts, so permabans of any kind pose no threat to this type of player.
Plus, Riot has issued instant permabans for feeding in the past. It's all a question of how extreme it is and maybe sometimes how obvious it is a smurf account with the sole purpose of trolling. If there is a good chance for somebody to reform, why would you risk pissing them off so hard that they turn into the type of player you can't properly control?
Now all that said, I voted yes on your poll. A season ranked ban seems appropriate. If we remove the season rewards (and thus the main point for ranked play) for boosters for one season when they are caught, I think it's appropriate to ban intentional feeders from ranked for one season.
I mean, ultimately both are a way of consistently skewing the ranked system... just that in one case you can take away the specific motivation for the behaviour rather than access to the entire thing.
