I understand where you're coming from. It is very frustrating when you get a string of games where it seems the troll or dcer is constantly on your team.
However, in the grand scheme of things these are basically random events and if you consider that if you are not going to troll then there are only 4 possible slots out of 9 on your team where there could be a troll or afk/disconnect. Basically, so long as you never troll go afk or disconnect then the the other team will get the troll about 55% of the time over the long run.
The biggest problem with your idea is that it rewards specific playing styles while punishing others. Tanks and supports for instance will often have a negative KDA even though they are playing well by peeling and even dying for their carries. In bronze league it is already tough to find queues where somebody actually WANTS to support. Introduce something like this and players will start working against each other even more than they already do. You think players rage about KS now, imagine with your system since KSing would be everybody's focus and nobody will be willing to be the guy that engages.
Your system also completely disregards objectives. You are trying to tell us that a jungler with a slightly negative KDA who was on top of map pressure and objective control all game should lose LP?
The more I think about it the more I am convinced that this would seriously break the game. Many junglers and supports would become unplayable if you wanted to gain elo.