With regard to Riot Ambassador's comment on a karma system, as shown below:
Originally Posted by Riot Ambassador
It’s an interesting suggestion for the system, but something we feel that could be easily exploitable by those with enough friends who can hand out free karma. It does bring up an interesting point though. Are there ways to reward positive game behavior in League of Legends in a manner that won’t be abused or exploited? We don’t really have a stance on this yet but it is something we’ve thought about.
Why not restrict karma voting (+ or - karma) to players who are not friends of the evaluated player? This would prevent friends from abusing the system and ensures that someone's karma is weighted only by those who do not interact with the evaluated player on a regular basis.
In light of the generally poor sportsmanship observed in the LoL community, it is very likely that a player will get significantly more karma downvotes than upvotes, due to:
1. Troll players who would want to abuse the system
2. Players just getting ticked off at someone for dominating them/winning an in-game debate/rivalry with them
3. Players have already been conditioned to recognize and report players who get on their nerves/display negative behavior, but have not been conditioned to recognize and praise-report players who display great sportsmanship/cooperation, as there is no incentive/reward for being a good sport apart from avoiding punishment.
For these reasons, karma upvotes should have 150-200% the value of karma downvotes. Displaying great sportsmanship would be much more rewarding due to this. Karma votes toward one player should only count once (i.e. cannot vote the same player's karma more than once).
Matchmaking should also be modified to weigh the karma of players being matched up, to match up players of similar karma, forcing trolls to have to face other trolls, hopefully as a form of reforming the player or something. New players should start with a set amount of positive karma so that they aren't immediately matched against trolls and whatnot.
TL;DR - Riot should implement the karma system. Only non-friends can vote on someone's karma so the system isn't abused, and karma downvotes hold less weight than upvotes, and karma should become a factor in matchmaking. New players start with positive karma to avoid matching up with trolls right off the bat.