You think all these people are purposely doing this to ruin the other player's game? Sure there are some that would, but most of the people actually have connection problems, and most of the time it's not on their end.
I've been playing since the beginning of S3, and I almost never had connection problems. Sure back then, I would get a random half second lag spike that goes away instantly, or have to relog once in every 50+ or so games but never anything big. I just got back to league about 2-3 weeks ago from a 2 month break, and I've been having all these random lag issues, attempting to reconnect on almost every game, and my usual average ping of around 87 would just stay at 250-300+ for almost all game.
It's not my connection itself, I can play other games that are way farther then League's servers with way less ping. My computer is definitely not cheap since I could play much more demanding games on High settings without any issues again.
It's not the players fault from all these disconnections, it's riot's server. So you think it's fair that they would be banned from ranked games just because riot can't fix their problems? Then again, people are getting banned on a normal basis because of the crappy servers, and all the response we get from riot is "Not our problem, it's on your end" (even though this is happening on a mass amount of players...)
Although I do agree some what on what your saying. If people think that they might lag because of the servers, they really shouldn't play ranked. I played 1 game of ranked last week and after that, I decided to just stick with normals and aram until this problem fixes itself. Sucks though, what a big disappointment for anyone who really really wanted to grind to a certain rankings right before the end of the season.